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Axilla

The axilla, also known as the armpit, is a pyramidal-shaped anatomical space situated beneath the glenohumeral joint at the junction between the upper limb and the lateral thoracic wall.^[1] This region serves as a conduit for critical neurovascular structures transitioning from the thorax to the arm, including the axillary artery, axillary vein, brachial plexus, and axillary lymph nodes.^[1] Its apex directs superiorly toward the root of the neck, bounded by the clavicle, first rib, and superior border of the scapula, while the base forms the axillary floor covered by skin, subcutaneous tissue, and axillary fascia.^[2] The axilla is delimited by four walls: anteriorly by the pectoralis major and minor muscles; posteriorly by the subscapularis, teres major, and latissimus dorsi; medially by the serratus anterior; and laterally by the intertubercular sulcus of the humerus, or bicipital groove.^[1] These boundaries enclose a compartment filled with loose connective tissue, fat, and lymphatics, facilitating arm movement while protecting vital conduits.^[3] The axillary artery, a continuation of the subclavian artery, supplies oxygenated blood to the upper limb and divides into three parts relative to the pectoralis minor muscle, giving rise to branches such as the superior thoracic, thoracoacromial, and lateral thoracic arteries.^[4] Complementing this, the axillary vein drains deoxygenated blood, and the brachial plexus cords reorganize within the axilla to innervate the arm's musculature and skin.^[1] Clinically, the axilla holds significance due to its lymphatic drainage, particularly the axillary lymph nodes, which filter lymph from the upper limb, breast, and chest wall, making them pivotal in staging and treating breast cancer through sentinel node biopsy or axillary dissection.^[5] Infections, such as hidradenitis suppurativa, and vascular injuries can arise here, underscoring the need for precise anatomical knowledge in surgical interventions like mastectomies or axillary artery repairs.^[1] The region's contents also render it susceptible to lymphadenopathy from systemic conditions, including malignancies and infections.^[5]

Anatomy

Boundaries and Apex

The axilla forms a pyramidal space between the upper limb and thoracic wall, characterized by four walls, a base formed by the axillary skin and fascia, and an apex directed superiorly toward the root of the neck.^[1]^[2] The anterior wall is primarily composed of the pectoralis major and pectoralis minor muscles, along with the overlying clavipectoral fascia, which extends from the clavicle to the floor of the axilla.^[1]^[2] The posterior wall consists of the subscapularis muscle superiorly, transitioning inferiorly to the teres major and latissimus dorsi muscles, forming a broad muscular layer adjacent to the scapula and humerus.^[1]^[2] The medial wall is formed by the serratus anterior muscle covering the lateral aspects of ribs 1 through 5, providing a thoracic boundary reinforced by the thoracic fascia.^[1] The lateral wall, the narrowest, corresponds to the intertubercular sulcus (bicipital groove) of the humerus, bounded by the insertions of the pectoralis major, teres major, and latissimus dorsi muscles.^[1]^[2] The apex, also termed the cervicoaxillary canal, represents the superior aperture of the axilla, measuring approximately 1-2 cm in diameter and serving as the conduit for the axillary artery, vein, and brachial plexus cords transitioning from the neck to the upper limb.^[6]^[7] It is bounded anteriorly by the clavicle and subclavius muscle, posteriorly by the superior border of the scapula, and inferiorly by the first rib's outer margin, creating a triangular interval that narrows superiorly.^[2]^[8] This apex facilitates the continuity of neurovascular structures while being reinforced by surrounding fascial septa, such as the axillary sheath, which envelops the major vessels and nerves.^[1] In clinical contexts, the apex's patency is critical for unobstructed flow, as compression here—due to trauma or masses—can impair upper limb perfusion and innervation.^[1]

Muscular and Fascial Contents

The muscular contents of the axilla encompass the muscles delineating its four walls and those traversing the region. The anterior wall is formed by the pectoralis major superiorly and pectoralis minor inferiorly, with the subclavius muscle contributing near the apex.^[2]^[1] The posterior wall consists of the subscapularis muscle superiorly, transitioning to the teres major and latissimus dorsi inferiorly.^[1]^[3] The medial wall is primarily the serratus anterior overlying the ribs and intercostal muscles of the thoracic wall.^[1]^[2] The lateral wall is narrow, formed by the coracobrachialis, short head of the biceps brachii, and the humerus in its intertubercular sulcus.^[1]^[3] Tendons of the short head of the biceps brachii and coracobrachialis traverse the axilla en route to their attachments on the coracoid process of the scapula.^[2] These muscles facilitate arm flexion, adduction, and related movements at the shoulder and elbow joints.^[1] Fascial contents include the axillary fascia, a dense fibrous sheet forming the floor or base of the axilla, extending between the pectoralis major anteriorly and latissimus dorsi posteriorly, and continuous with the deep fascia of the arm and chest wall.^[9]^[3] The clavipectoral fascia, also known as the suspensory ligament of the axilla, invests the subclavius and pectoralis minor muscles, forming the medial wall of the clavipectoral triangle through which the cephalic vein and lateral pectoral nerves pass.^[2] These fascial layers provide structural support and compartmentalize the neurovascular elements within the axilla.^[1]

Neurovascular Structures

The neurovascular structures of the axilla primarily consist of the axillary artery, axillary vein, and the cords and branches of the brachial plexus, which traverse the region embedded within axillary fat and fascia.^[10] These elements form a compact bundle that supplies blood to and drains from the upper limb while providing motor and sensory innervation.^[2] The axillary artery lies centrally, with the vein positioned medial to it and the brachial plexus cords arranged around the artery—lateral, medial, and posterior cords corresponding to their relation to the artery.^[3] The axillary artery originates as the continuation of the subclavian artery at the lateral border of the first rib and terminates as the brachial artery at the inferior border of the teres major muscle.^[4] It is divided into three parts by the pectoralis minor muscle: the first part (proximal to the muscle) gives off the superior thoracic artery; the second part (behind the muscle) branches the thoracoacromial and lateral thoracic arteries; and the third part (distal to the muscle) produces the subscapular artery (with its thoracodorsal branch), as well as the anterior and posterior circumflex humeral arteries.^[11] These branches supply the chest wall, shoulder girdle, and proximal arm musculature.^[12] The axillary vein parallels the artery, lying anteromedial to it, and is formed by the confluence of the basilic and brachial veins at the inferior margin of the teres major.^[13] It receives tributaries that generally mirror the arterial branches, including the cephalic vein via the lateral aspect, and terminates as the subclavian vein at the lateral border of the first rib.^[2] This vein provides venous drainage for the upper limb and lateral thoracic wall.^[14] The brachial plexus enters the axilla after passing through the scalene muscles and subclavian artery, reorganizing into three cords around the axillary artery.^[15] The lateral cord (C5-C7) gives rise to the lateral pectoral nerve, musculocutaneous nerve, and lateral root of the median nerve; the medial cord (C8-T1) contributes the medial pectoral nerve, medial cutaneous nerves of the arm and forearm, ulnar nerve, and medial root of the median nerve; the posterior cord (C5-T1) branches the upper and lower subscapular nerves, thoracodorsal nerve, axillary nerve, and radial nerve.^[16] These nerves innervate the shoulder, arm, forearm, and hand muscles, as well as providing cutaneous sensation to the upper limb.^[17] Additional nerves, such as the long thoracic nerve (piercing the serratus anterior) and intercostobrachial nerve (from T2), course through the axilla but are not primary components of the brachial plexus bundle.^[18]

Lymphatic Components

The axillary lymph nodes, embedded in the fatty tissue of the axilla, consist of 20 to 40 nodes organized into five distinct groups based on their anatomical position and afferent drainage: the pectoral (anterior), subscapular (posterior), humeral (lateral), central, and apical groups.^[19]^[5] The pectoral group comprises 3 to 5 nodes located along the inferior border of the pectoralis minor muscle in the anterior axillary wall, primarily receiving lymph from the breast and anterior thoracic wall.^[20] The subscapular group includes 6 to 7 nodes positioned posterior to the axillary vein along the subscapular artery and vein, draining the posterior thoracic wall and scapular region.^[20] The humeral (or lateral) group features 4 to 6 nodes lateral to the axillary vein, collecting lymph from the upper limb via superficial and deep lymphatic vessels that parallel the cephalic and basilic veins.^[20]^[5] The central group, consisting of 3 to 4 nodes at the base of the axilla embedded in adipose tissue, receives efferent vessels from the pectoral, subscapular, and humeral groups, serving as an intermediate filtration station.^[21] The apical group, with 1 to 2 nodes at the apex of the axilla superior to the pectoralis minor muscle, integrates efferents from the central group and directly from surrounding structures, channeling lymph toward the subclavian lymphatic trunk, which ultimately joins the thoracic duct on the left or the right lymphatic duct on the right to enter the venous system at the jugular-subclavian junction.^[20]^[5] This hierarchical drainage pathway ensures sequential filtration of lymph from the upper quadrant of the trunk, upper limb, and mammary gland, with lymphatic vessels accompanying neurovascular structures through the axillary sheath.^[21] Overall, the axillary nodes filter pathogens and antigens, facilitating immune surveillance, though their precise node counts can vary individually due to anatomical differences.^[5]

Physiology

Sweat Glands and Secretion Mechanisms

The axilla contains a high density of sweat glands, including eccrine, apocrine, and apoeccrine types, which contribute to both thermoregulation and localized odor production. Eccrine glands predominate across the body but are present in the axilla alongside the others, secreting a clear, watery fluid primarily for evaporative cooling.^[22] Apocrine glands are concentrated in the axillary region, opening into hair follicles rather than directly onto the skin surface, and produce a thicker, milky secretion rich in lipids, proteins, and steroids that remains odorless until metabolized by cutaneous bacteria.^[23] In the axilla, the ratio of apocrine to eccrine glands approximates 1:1, contrasting with 1:10 in other body regions, reflecting specialized regional adaptations. Apoeccrine glands, a hybrid form derived from eccrine precursors, emerge post-puberty and can constitute up to 45% of total axillary glands by late adolescence, secreting high volumes of watery fluid responsive to cholinergic stimuli.^[24] Eccrine gland secretion operates via a merocrine mechanism, where secretory cells release hypotonic sweat through exocytosis without cellular disruption; the process begins with isotonic fluid production in the coiled secretory portion, followed by sodium and chloride reabsorption in the duct to yield a final electrolyte concentration of approximately 20-60 mEq/L sodium.^[22] This is triggered by sympathetic cholinergic innervation in response to thermal or emotional stimuli, with acetylcholine binding to muscarinic receptors on myoepithelial cells to propel secretion.^[25] Apocrine secretion, by contrast, involves true apocrine release: formation of an apical cytoplasmic cap enriched with Golgi-derived vesicles, followed by membrane invagination and pinching off of the cap, delivering cellular material including membrane-bound lipids into the ductal lumen.^[26] This process is primarily adrenergically mediated via catecholamines, with peak activity post-puberty under stress or hormonal influence, though the glands remain inactive until then.^[27] Apoeccrine glands employ a merocrine-like mechanism similar to eccrine but exhibit enhanced cholinergic sensitivity, enabling rapid, high-output responses that amplify overall axillary perspiration.^[24] The composite axillary sweat thus blends thermoregulatory (eccrine and apoeccrine) and potentially signaling (apocrine) functions, with bacterial decomposition of apocrine lipids—such as straight-chain fatty acids—generating volatile compounds responsible for body odor, a process absent in isolated sterile secretions. Myoepithelial contractions, induced by autonomic signals, facilitate expulsion across all gland types, ensuring efficient delivery despite the axilla's occluded environment.^[25] Disruptions in these mechanisms, such as excessive cholinergic drive, underlie conditions like axillary hyperhidrosis, where eccrine and apoeccrine outputs predominate.^[22]

Sensory and Motor Functions

The skin of the axilla receives primary sensory innervation from the intercostobrachial nerve, a lateral cutaneous branch of the second intercostal nerve (T2), which supplies sensation to the axillary floor and adjacent medial upper arm.^[28] This nerve frequently communicates with the medial cutaneous nerve of the arm (from the medial cord of the brachial plexus, T1-T2), providing overlapping sensory coverage to the medial arm and inferolateral axilla.^[29] Minor contributions may arise from thoracic intercostal nerves or the lateral pectoral nerve for the anterior axillary fold.^[30] Motor functions in the axilla involve branches of the brachial plexus cords, which innervate muscles forming its boundaries and facilitate upper limb movement. The lateral pectoral nerve (C5-C7, from lateral cord) supplies the clavicular head of pectoralis major, aiding arm flexion and adduction, while the medial pectoral nerve (C8-T1, from medial cord) innervates pectoralis minor and sternocostal pectoralis major for scapular stabilization and arm depression.^[17] The thoracodorsal nerve (C6-C8, from posterior cord) provides motor supply to latissimus dorsi, enabling arm extension, adduction, and internal rotation.^[16] Upper and lower subscapular nerves (posterior cord, C5-C7) innervate subscapularis for internal rotation and teres major for adduction and extension.^[17] The long thoracic nerve (C5-C7, from roots) pierces the axilla to supply serratus anterior, essential for scapular protraction and arm elevation.^[31] The axillary nerve (C5-C6, posterior cord terminal branch) motors deltoid for abduction and teres minor for external rotation.^[32] These innervations collectively support shoulder girdle stability and proximal arm motility.

Lymphatic Drainage Dynamics

The axillary lymph nodes, typically numbering 20 to 30, are embedded in the axillary fat pad and grouped into anterior (pectoral), posterior (subscapular), lateral (humeral), central, and apical sets, with further subdivision into levels I (lateral to pectoralis minor), II (posterior to it), and III (medial to it).^[5] These nodes receive afferent lymphatic vessels primarily from the upper limb (superficial vessels following the cephalic and basilic veins to cubital and then humeral nodes, deep vessels paralleling arteries), lateral breast quadrants, anterior and posterior thoracic walls, and upper abdominal wall above the umbilicus.^[5]^[20] Lymph percolates through the nodal sinuses—subcapsular, cortical, and medullary—for filtration of interstitial fluid, cellular debris, and antigens before exiting via efferent vessels; the central nodes consolidate input from peripheral groups, channeling it to apical nodes.^[5] Lymph flow through the axilla relies on a combination of intrinsic and extrinsic propulsion mechanisms, as lymphatic vessels lack a central pump analogous to the heart.^[33] Intrinsic propulsion arises from rhythmic phasic contractions of smooth muscle in collecting lymphatic vessel walls, generating pressure gradients to drive fluid forward against hydrostatic opposition, with one-way valves preventing backflow.^[34] Extrinsic factors enhance this in the axilla, including compression from skeletal muscle contractions during arm and shoulder movements (e.g., abduction or flexion), respiratory excursions affecting thoracic pressure, and pulsatile forces from the adjacent axillary artery.^[33]^[20] These dynamics ensure efficient clearance of approximately 2-4 liters of lymph produced daily body-wide, though axilla-specific volumes vary with activity and hydration.^[33] Efferent vessels from apical axillary nodes converge into the subclavian lymphatic trunk, which drains left-sided flow via the thoracic duct and right-sided via the right lymphatic duct, ultimately emptying into the venous system at the jugular-subclavian vein junction.^[5]^[33] This unidirectional pathway supports immune surveillance by concentrating lymphocytes and macrophages in nodes for antigen processing, while maintaining interstitial fluid homeostasis; disruptions, such as from immobility, can impair flow and lead to localized edema.^[33] In physiological states, upper limb activity—quantified in studies as increasing flow rates by up to 10-20 fold through muscle pumping—optimizes axillary drainage efficiency.^[34]

Clinical Significance

Infections and Dermatoses

The axilla, with its moist environment, apocrine sweat glands, and hair follicles, predisposes to various infections and inflammatory dermatoses, often exacerbated by occlusion, friction, and bacterial overgrowth.^[35] Common presentations include recurrent abscesses, erythematous plaques, and pustules, which may require differentiation via clinical exam, Wood's lamp, or culture to guide therapy.^[36] Hidradenitis suppurativa (HS), a chronic inflammatory disorder of the pilosebaceous-apocrine unit, frequently manifests in the axilla as the primary site, affecting up to 70-90% of cases.^[37] Global prevalence ranges from 0.1% to 4%, with onset typically post-puberty and higher incidence in females and those with obesity or smoking history.^[38] Initial lesions appear as painful, pea-sized subcutaneous nodules that evolve into abscesses, draining sinuses, and scarring fistulas over weeks to months, driven by follicular occlusion and immune dysregulation rather than primary infection, though secondary bacterial involvement (e.g., Staphylococcus aureus) is common.^[39] ^[37] Severity is staged by Hurley criteria, with axillary involvement often leading to restricted arm movement and chronic pain.^[37] Intertrigo, a superficial inflammatory dermatitis in flexural areas like the axilla, arises from maceration, heat, and friction, creating a milieu for secondary candidal or bacterial superinfection in 20-30% of cases.^[36] Clinically, it presents as symmetric, weeping erythema with satellite pustules if fungal, or crusting if bacterial, particularly in obese or diabetic individuals where axillary folds trap moisture.^[36] Management emphasizes barrier creams (e.g., zinc oxide) and topical antifungals like nystatin for Candida albicans, applied twice daily until resolution, alongside weight reduction to mitigate recurrence.^[36] Bacterial folliculitis, often staphylococcal, targets axillary hair follicles post-shaving or depilation, yielding pruritic papulopustules that may coalesce into furuncles or carbuncles.^[40] Fungal variants, such as Malassezia folliculitis, present as uniform itchy papules without comedones, distinguishable by potassium hydroxide prep showing yeast spores.^[40] Treatment involves topical antibacterials (e.g., mupirocin) or antifungals (e.g., ketoconazole) for 1-2 weeks, with incision for larger abscesses.^[40] Erythrasma, caused by Corynebacterium minutissimum, manifests as asymptomatic, sharply demarcated brown-red patches in the axilla, with fine scaling and occasional mild pruritus.^[41] Diagnosis relies on coral-red fluorescence under Wood's lamp due to bacterial porphyrins, confirmed rarely by microscopy revealing filamentous rods.^[41] It responds to topical erythromycin or oral clarithromycin over 5-14 days, with low recurrence if hygiene is maintained.^[41] Differential includes tinea or psoriasis, but lack of scaling or fluorescence aids distinction.^[41]

Neoplastic Involvement

The axilla is most commonly affected by metastatic neoplasms, particularly in the lymph nodes, with breast carcinoma accounting for the majority of cases due to lymphatic drainage patterns from the breast. Axillary lymph node involvement occurs in approximately 20-40% of early-stage breast cancers and up to 70-90% in advanced stages, serving as a key prognostic indicator that influences staging and treatment decisions such as axillary lymph node dissection or sentinel node biopsy.^[42]^[43] Micrometastases (≤2 mm) in a single node confer a modestly increased risk of distant recurrence compared to node-negative disease, though outcomes vary by tumor biology and adjuvant therapies.^[44] Other metastatic sources include melanoma (via lymphatic spread from cutaneous sites), ovarian carcinoma (as a common non-mammary primary for axillary metastases), and less frequently lung, gastric, or thyroid adenocarcinomas, with histology guiding primary site identification in up to 80% of cases through immunohistochemistry.^[45]^[46] Contralateral axillary involvement in breast cancer, seen in <1% of cases, typically represents locoregionally advanced disease rather than distant metastasis, often linked to aberrant lymphatics or prior interventions.^[47]^[48] Lymphoma, including Hodgkin and non-Hodgkin subtypes, can present with axillary adenopathy as a primary manifestation, with bilateral involvement suggesting systemic disease over localized metastasis.^[49] Primary neoplasms of the axilla are exceedingly rare, comprising <1% of axillary masses, and often arise from ectopic tissues or adnexal structures rather than native axillary components. Accessory (ectopic) breast tissue, present in 1-6% of the population and most frequently located in the axilla (60-70% of ectopic sites), can develop invasive ductal carcinoma histologically identical to orthotopic breast cancer, representing <1% of all breast malignancies.^[50]^[51] Sweat gland-derived tumors, such as primary mucinous adenocarcinoma of the skin, occur predominantly in the axilla among apocrine-rich areas, with fewer than 150 cases reported globally and a predilection for local recurrence post-excision.^[52] Other primaries include cutaneous myoepithelial carcinoma and soft tissue sarcomas, which may mimic metastatic disease on imaging but require histopathological confirmation for differentiation.^[53] Cancers of unknown primary (CUP) presenting as isolated axillary lymphadenopathy, often adenocarcinomas, are managed presumptively as occult breast cancer if estrogen receptor-positive or HER2-expressing, with 5-year survival rates of 60-80% following mastectomy, axillary dissection, and systemic therapy, though primary identification remains elusive in 20-30% of cases.^[55] Imaging modalities like ultrasound and MRI detect nodal involvement with sensitivities of 70-90%, but fine-needle aspiration or core biopsy is essential for cytological verification, as clinical palpation alone underestimates metastasis in up to 67% of suspicious nodes.^[56]

Surgical and Interventional Procedures

Axillary lymph node dissection (ALND) is a surgical procedure that removes lymphatic tissue from levels I, II, and sometimes III of the axilla to stage breast cancer and treat nodal metastases.^[58] Typically, 10 to 30 lymph nodes are excised, with level I nodes lying lateral to the pectoralis minor muscle, level II behind it, and level III medial.^[59] This approach, historically standard for clinically node-positive disease, carries risks including lymphedema (affecting up to 20% of patients), nerve injury, and seroma formation.^[60] Sentinel lymph node biopsy (SLNB) offers a targeted alternative for early-stage breast cancer, identifying and removing the first 1-3 draining nodes using peritumoral injection of technetium-99m colloid and/or isosulfan blue dye, followed by intraoperative gamma probe detection or visual inspection.^[61] With a false-negative rate below 10% in validated protocols, SLNB reduces morbidity compared to ALND while accurately staging the axilla in node-negative cases, guiding decisions on adjuvant therapy.^[62] It has supplanted routine ALND in clinically node-negative patients since trials like ACOSOG Z0011 demonstrated equivalent survival with whole-breast radiation.^[63] Percutaneous axillary artery access facilitates large-bore endovascular interventions, such as transfemoral-inaccessible transcatheter aortic valve replacement or mechanical circulatory support, by puncturing the second segment under ultrasound guidance with the arm abducted.^[64] Closure devices or surgical cutdown mitigate risks like hematoma (5-10%) or arterial dissection, positioning it as a viable upper extremity alternative to radial or brachial routes.^[65] For severe primary axillary hyperhidrosis unresponsive to topicals, botulinum toxin type A (onabotulinumtoxinA) injections, dosed at 50-100 units per axilla in 15-20 intradermal sites, inhibit cholinergic sweat gland stimulation, yielding 82-87% sweat reduction lasting 4-14 months.^[66] Starch-iodine mapping pre-injection ensures precise targeting of hyperactive areas, with repeat treatments possible but diminishing efficacy over time due to antibody formation in some cases.^[67]

Evolutionary Perspectives

Apocrine Gland Development and Pheromonal Hypotheses

Apocrine sweat glands in the human axilla originate from the ectodermal layer during fetal development, with precursors detectable as early as the fifth month of gestation in axillary skin, though they differ from eccrine glands by forming later and in association with pilosebaceous units rather than independently.^[68] These glands are present in a rudimentary form at birth across a broader bodily distribution, but undergo regression postnatally to become concentrated in hair-bearing regions such as the axilla and groin.^[69] Secretory activity remains dormant until puberty, when androgens stimulate maturation and function, leading to the production of viscous, protein-rich secretions that are initially odorless but become volatile upon bacterial decomposition by skin microbiota.^[22] Hypotheses regarding pheromonal roles posit that axillary apocrine secretions function as chemical signals modulating interpersonal attraction, mood, and reproductive physiology, analogous to apocrine-derived scents in nonhuman mammals.^[70] Specific steroidal compounds, such as androstadienone extracted from male axillary glands, have been shown in controlled studies to elevate positive mood, heighten focus on emotional cues, and influence luteinizing hormone pulsatility in female recipients, suggesting potential modulator effects on hypothalamic-pituitary function.^[71]^[72] Proponents argue these effects arise from odor precursors transformed by resident bacteria, with axillary density of apocrine glands (up to 500-600 per cm²) facilitating signal dissemination via volatiles.^[73] However, empirical support for designating these secretions as true pheromones—defined by species-specific, involuntary behavioral or physiological responses via dedicated sensory pathways—remains inconclusive, as human vomeronasal organs are vestigial and studies often rely on subjective self-reports or small samples prone to methodological artifacts like olfactory habituation.^[74] Reviews of axillary extract experiments highlight inconsistent replication across populations and contexts, attributing observed synchrony effects (e.g., menstrual cycle alignment) more plausibly to social cues than isolated chemicals, underscoring the need for rigorous, blinded trials isolating causal volatiles from confounding sensory inputs.^[75]^[76] While apocrine glands' evolutionary conservation implies adaptive signaling, current data favor idiomatic odor-based individual recognition over stereotyped pheromonal mediation in humans.^[75]

Axillary Hair and Odor Production

Axillary hair emerges during puberty under the influence of androgens, which transform vellus hairs into coarser terminal hairs in the axilla.^[77] This development typically occurs around ages 10-15 in both sexes, coinciding with adrenarche and increased adrenal androgen production.^[78] The hair follicles in the axilla are androgen-sensitive, leading to denser growth in males due to higher testosterone levels, though females also exhibit axillary hair.^[79] Odor production in the axilla arises primarily from apocrine sweat glands, concentrated in hairy regions, which secrete a viscous, odorless fluid rich in lipids, proteins, and steroids.^[80] This secretion is broken down by resident skin bacteria, such as Corynebacterium and Staphylococcus species, into volatile organic compounds like 3-methyl-2-hexenoic acid, responsible for the characteristic axillary scent.^[81] Eccrine glands contribute aqueous sweat that facilitates bacterial activity but does not directly produce odorants.^[82] Axillary hair enhances odor intensity by providing a moist, occluded environment that promotes bacterial colonization and retention of apocrine secretions.^[83] Experimental shaving reduces perceived odor intensity and increases pleasantness ratings temporarily, as hair removal disrupts bacterial biofilms and improves ventilation.^[84] However, regrowth restores baseline odor levels within weeks, indicating hair's role in amplifying rather than initiating malodor.^[85] From an evolutionary standpoint, axillary hair and associated odors may function in pheromonal signaling, potentially influencing mate attraction or social bonding through volatile compounds that convey genetic compatibility, such as major histocompatibility complex (MHC) variation.^[71] Hypotheses suggest the axillary region evolved as a specialized odor-dispersing organ, with hair aiding in wicking and volatilizing secretions to strengthen pair bonds or advertise reproductive status, though human pheromone effects remain debated due to limited direct evidence compared to other mammals.^[86] Empirical studies link certain axillary volatiles to modulated mood and sexuality in recipients, supporting a subtle chemosensory role.^[71]

Sociocultural Aspects

Grooming Practices and Hygiene Implications

Grooming practices for the axilla primarily involve hair removal methods such as shaving, waxing, chemical depilation, and laser treatments, aimed at reducing visible hair and associated odor. Shaving, the most common method, uses a razor to cut hair at skin level, while waxing pulls hair from the root, providing longer-lasting results typically 3-6 weeks. Laser hair removal targets hair follicles with light energy to inhibit regrowth, often requiring multiple sessions over months for semi-permanent effects. These practices are widespread, with surveys indicating over 80% of women and increasing numbers of men in Western societies engage in axillary hair removal for aesthetic and hygiene reasons.^[83] Hygiene implications stem from the axilla's high density of apocrine glands, which produce sweat that bacteria metabolize into odorous compounds; axillary hair increases surface area for bacterial adhesion and traps moisture, fostering microbial growth such as Corynebacterium species responsible for odor. A 2015 clinical study on men found that shaving combined with soap washing reduced axillary odor more effectively than washing alone, as hair shafts retain secretions that serve as a medium for bacterial proliferation. Similarly, a 2016 study reported that shaving significantly lowered odor intensity for up to 24 hours post-removal by minimizing bacterial substrates.^[83]^[87] While hair removal does not alter sweat gland activity or total perspiration volume, it enhances evaporation by reducing moisture retention in hair, potentially decreasing perceived wetness and bacterial odor without increasing infection risk when performed hygienically. Trimming to 0.75-1 inch preserves some barrier function against friction while limiting bacterial habitats, though improper shaving can cause micro-abrasions leading to temporary irritation or folliculitis. Regular washing with antibacterial soaps complements grooming by directly reducing microbial load, underscoring that hygiene benefits arise from combined mechanical removal of hair and debris rather than grooming alone.^[88]^[89]^[90]

Cultural Norms on Odor and Hair

In ancient Egyptian society, removal of axillary hair was practiced by both sexes to promote cleanliness and purity, as body hair was associated with uncleanliness, a norm reinforced through grooming rituals dating back to at least 3000 BCE.^[91] Similarly, biblical texts such as Leviticus prescribed full body shaving for ritual purification, including in cases of skin conditions, reflecting early associations between axillary hair and potential disgust or impurity in Judeo-Christian traditions.^[92] Modern Western norms, particularly in the United States, shifted toward routine axillary hair removal for women around 1914, coinciding with sleeveless fashion trends that exposed underarms and advertising campaigns linking hairlessness to femininity, hygiene, and grooming standards.^[93] This practice extended to men more variably, often tied to odor management, as axillary hair traps sweat and bacteria, intensifying apocrine-derived body odor, though shaving yields only transient reductions in perceived odor unpleasantness, lasting weeks before regrowth restores baseline levels.^[83]^[84] Deodorant use proliferated in the 20th century as a cultural response to evolving hygiene ideals, where natural body odor became stigmatized among urban elites, associating it with lower social class rather than inherent unhealthiness.^[94] Cross-culturally, attitudes vary significantly; East Asian populations, where 80-95% exhibit a genetic variant in the ABCC11 gene reducing apocrine secretions and thus body odor, show lower deodorant adoption and less emphasis on axillary hair removal compared to Westerners.^[95] In parts of Europe, such as France, axillary hair retention among women is more normalized, complementing acceptance of milder natural odors without strong cultural aversion, contrasting with American preferences for shaved underarms rated as more attractive due to subdued scent intensity.^[96]^[85] These norms reflect gene-culture coevolution, where odor sensitivity influences grooming but is amplified by socioeconomic factors like access to bathing and products, rather than universal disgust.^[94]

Sensory Responses Including Tickling

The cutaneous innervation of the axilla derives mainly from the intercostobrachial nerve, a sensory branch of the second intercostal nerve (T2 dermatome), which supplies the skin of the axillary fossa and adjacent medial upper arm.^[3] Supplementary sensation arises from the medial cutaneous nerve of the arm (from the medial cord of the brachial plexus) and, to a lesser extent, the lateral cutaneous branches of the upper intercostal nerves.^[1] This neural supply includes a density of mechanoreceptors, such as Meissner's corpuscles for fine touch discrimination and hair follicle-afferent endings, contributing to the region's acute tactile sensitivity.^[1] Tickling in the axilla typically manifests as gargalesis, a laughter-inducing response to repeated, unpredictable light stroking or poking, distinct from knismesis (subtle itching-like crawling).^[98] The axilla ranks among the most ticklish body sites, alongside the soles and ribs, due to its thin, hair-bearing skin and proximity to unprotected neurovascular elements, prompting rapid withdrawal reflexes.^[99] Neurophysiologically, tickle stimuli activate low-threshold C-fiber mechanoreceptors and Aδ afferents, transmitting via spinothalamic tracts to elicit somatosensory cortical processing, hypothalamic involvement in autonomic arousal (e.g., increased heart rate and skin conductance), and motor inhibition-release patterns that generate laughter and evasion within 0.5 seconds.^[100] ^[101] Self-induced touch in this area rarely provokes tickling, as predictive cerebellar forward models suppress the response by integrating efference copies of intended movements.^[100] Variability in axillary ticklishness correlates with stimulus intensity, speed, and interpersonal dynamics; lighter, erratic touches heighten responses compared to steady pressure, which may desensitize via habituation.^[100] Evolutionary accounts posit that such sensitivity fosters defensive training in juveniles, conditioning reflexive protection of the axilla's vulnerable contents—including the brachial plexus, axillary artery, and lymphatics—against potential threats like arthropod vectors or physical intrusion.^[101] Empirical support derives from observational studies linking ticklish areas to embryonically "softer" zones with sparse protective hair or fat, though direct causal evidence remains correlative.^[102]

References

[1]
Anatomy, Shoulder and Upper Limb, Axilla - StatPearls - NCBI - NIH
The axilla is an anatomical region under the shoulder joint where the arm connects to the shoulder. It contains a variety of neurovascular structures.
[2]
The Axilla Region - Borders - Contents - TeachMeAnatomy
Sep 27, 2024 · The axilla is the name given to an area that lies underneath the glenohumeral joint, at the junction of the upper limb and the thorax.
[3]
Axillary region: Anatomy, contents and borders - Kenhub
The axilla is a three dimensional pyramidal space which changes shape due to its location and arm movement. Its apex is bound superiorly by the root of the neck ...
[4]
Anatomy, Shoulder and Upper Limb, Axillary Artery - StatPearls - NCBI
Jan 20, 2025 · The axillary artery is the main blood supply for the upper limb, starting from the subclavian artery and divided into 3 parts by the pectoralis ...Missing: contents | Show results with:contents
[5]
Anatomy, Shoulder and Upper Limb, Axillary Lymph Nodes - NCBI
The axilla is a pyramidal shaped area with five anatomical borders, based mainly on the musculature in this region [1]: Medial border: the serratus anterior ...
[6]
Axilla - Anatomy - News-Medical
The axilla is the space in the interval marking the junction of the upper arm and the chest wall. It is a key area because many important neurovascular ...
[7]
Anatomy of the axilla: Video, Causes, & Meaning - Osmosis
The axilla is shaped like a pyramid that has an apex, a base, and four walls. The apex of the axilla is also called the cervico-axillary canal, which is the ...
[8]
Axilla | Radiology Reference Article - Radiopaedia.org
Sep 5, 2013 · The axilla is pyramidal in shape with its apex opening superiorly towards the base of the neck between the subclavius muscle, first rib, ...
[9]
Axillary fascia - e-Anatomy - IMAIOS
The axillary fascia is a dense, fibrous sheet that forms the floor, or base, of the axilla (armpit). It is continuous with the deep fascia of the ...
[10]
Anatomy, Shoulder and Upper Limb, Axilla | Point of Care - StatPearls
Jul 24, 2023 · The humerus, the coracobrachialis, and the short head of the biceps form the lateral wall. The pectoralis major and minor muscles make up the ...
[11]
Axillary artery: Anatomy, branches and mnemonics - Kenhub
Mar 9, 2015 · Axillary artery · Course · Branches. Superior thoracic artery; Thoracoacromial artery; Lateral thoracic artery; Subscapular artery; Circumflex ...
[12]
https://teachmeanatomy.info/upper-limb/vessels/arteries/
[13]
Axillary vein: Anatomy, tributaries, drainage | Kenhub
The axillary vein is a deep vein of the upper limb that is formed by the union of the brachial and basilic veins. It starts at the lower border of the teres ...
[14]
Axillary vein | Radiology Reference Article | Radiopaedia.org
Mar 1, 2017 · The axillary vein is one of the major veins of the upper limb. It is formed by the union of the paired brachial veins and the basilic vein.
[15]
The Brachial Plexus - Sections - Branches - TeachMeAnatomy
Feb 10, 2025 · In the axilla and the proximal aspect of the upper limb, the three cords give rise to five major branches. These nerves continue into the upper ...
[16]
Brachial plexus: Anatomy, branches and mnemonics - Kenhub
The posterior cord extends into the radial nerve and axillary nerve. The medial cord extends into the ulnar nerve and the medial root of the median nerve.
[17]
Anatomy, Head and Neck: Brachial Plexus - StatPearls - NCBI - NIH
The 5 terminal branches of the brachial plexus are the musculocutaneous, median, ulnar, axillary, and radial nerves. The musculocutaneous nerve (C5-C7) is ...
[18]
Axilla | Radiology Reference Article - Radiopaedia.org
Sep 5, 2013 · Contents · vessels. axillary artery and branches. axillary vein and branches · nerves. brachial plexus · long thoracic nerve · axillary lymph nodes.
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Axillary Lymph Nodes Anatomy, Diagram & Function | Body Maps
They are about 1cm in size and are arranged into five groups: subscapular axillary (posterior), apical (medial or subclavicular), pectoral axillary (anterior), ...
[20]
Lymphatic Drainage of the Upper Limb - Vessels - Nodes - TeachMeAnatomy
### Summary of Lymphatic Drainage of the Upper Limb
[21]
Axillary lymph nodes: Definition, anatomy and location - Kenhub
The axillary lymph nodes are a collection of 5 groups of lymph nodes found in the axillary region of the upper limb.
[22]
Anatomy, Skin Sweat Glands - StatPearls - NCBI Bookshelf
Both eccrine and apocrine sweat glands originate from the epidermis. Eccrine glands begin as epithelial cellular buds that grow into the underlying mesenchyme.
[23]
Apocrine Glands Function & Location - Cleveland Clinic
Aug 22, 2024 · Apocrine glands are structures within your skin that produce and secrete different bodily substances like thick, oily sweat and earwax.
[24]
Full article: Physiology of sweat gland function: The roles of ...
Apoeccrine glands develop from eccrine sweat glands between the ages of ~8 to 14 years and increase to as high as 45% of the total axillary glands by age 16–18 ...
[25]
Structure and function of the sweat glands - Kenhub
Eccrine glands are found all over the body and secrete a watery product that cools the skin. · Apocrine sweat glands are mainly found in the armpits and perianal ...
[26]
proteins involved in the apocrine secretory mechanism - PubMed
The apocrine secretory mechanism is a mode of secretion by which the apical part of the cell cytoplasm is pinched off, which leads to the formation of an ...
[27]
Secretion from Human Apocrine Glands: An Electron Microscopic ...
In the apocrine type of secretion three stages were observed: (1) formation of an apical cap; (2) formation of a dividing membrane at the base of the apical ...
[28]
Anatomy, Shoulder and Upper Limb, Cutaneous Innervation - NCBI
Cutaneous innervation of the shoulder and upper limb comes from multiple peripheral nerves originating from cervical and thoracic nerve roots.Introduction · Structure and Function · Nerves
[29]
Origin, Branching, and Communications of the Intercostobrachial ...
Mar 17, 2017 · The ICBN functions to innervate portions of the axilla, tail of the breast, lateral chest wall and medial side of the arm [2-3]. The ICBN, in ...
[30]
Intercostobrachial Nerve - an overview | ScienceDirect Topics
The intercostobrachial nerve (ICBN) joins the MBCN when it enters the axilla. The ICBN is the lateral cutaneous branch of the second intercostal nerve. As the ...
[31]
Brachial Plexus - Physiopedia
The brachial plexus passes from the neck to the axilla and supplies the upper limb. It is formed from the ventral rami of the 5th to 8th cervical nerves.Introduction · Description · Injuries · Mechanism of Injury<|control11|><|separator|>
[32]
Anatomy, Shoulder and Upper Limb, Axillary Nerve - StatPearls - NCBI
The axillary nerve begins at the ventral rami of C5 and C6 spinal nerves and continues as the smaller branch of the posterior cord of the brachial plexus.
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Anatomy, Lymphatic System - StatPearls - NCBI Bookshelf - NIH
Mar 6, 2023 · Components of the lymphatic system include lymph, lymphatic vessels and plexuses, lymph nodes, lymphatic cells, and a variety of lymphoid organs.Missing: dynamics | Show results with:dynamics
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Lymphatic pumping: mechanics, mechanisms and malfunction - PMC
The robust contractions of lymphatic muscle cells are the driving force for active lymph propulsion against adverse pressure gradients (Zweifach & Prather, 1975) ...
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Axillary manifestations of dermatologic diseases: a focused review
This review categorizes the various conditions based on their inflammatory or infectious etiology and describes each condition based on their predominant ...
[36]
Intertrigo - StatPearls - NCBI Bookshelf - NIH
Oct 28, 2024 · Intertrigo is a superficial inflammatory skin condition that affects flexural surfaces, such as the axillae, abdominal folds, and perineum. ...
[37]
Hidradenitis Suppurativa - StatPearls - NCBI Bookshelf
May 6, 2024 · Hidradenitis suppurativa is a chronic inflammatory skin condition characterized by painful lesions such as deep-seated nodules, abscesses, skin tunnels, and ...
[38]
Hidradenitis Suppurativa (Acne Inversa) - DermNet
Who gets hidradenitis suppurativa? The global prevalence of hidradenitis suppurativa is estimated to range from 0.1% to 4%. However, underdiagnosis and ...Management of hidradenitis... · PAPA syndrome · Crohn skin disease
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Hidradenitis suppurativa - Symptoms and causes - Mayo Clinic
Mar 21, 2025 · Hidradenitis suppurativa is more common and severe in people who are overweight. It also has an association with severe acne, arthritis, ...Missing: dermatoses | Show results with:dermatoses
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Folliculitis - StatPearls - NCBI Bookshelf - NIH
Aug 8, 2023 · Even so, folliculitis may also result from fungal or viral infections, but this does not mean that all folliculitis cases are infectious.
[41]
Erythrasma - StatPearls - NCBI Bookshelf
A biopsy is rarely needed for the diagnosis of erythrasma. Examination of the skin by microscopy would show rod-like organisms in the horny layer. However, ...
[42]
Axillary lymph nodes and breast cancer: a review - PubMed
Results: The risk of axillary lymph node involvement is substantial for most patients, even those with small tumors. The morbidity resulting from a careful ...<|separator|>
[43]
Axillary lymph node metastases in breast cancer - PubMed
Metastatic involvement of axillary lymph nodes is one of the most important prognostic variables in breast cancer. The aim of our work was to study the ...
[44]
Minimal axillary lymph node involvement in breast cancer ... - PubMed
The presence of a single micrometastatic lymph node is associated with a higher risk of distant recurrence as compared to node-negative disease only for ...
[45]
Non-mammary metastases to the breast and axilla: a study of 85 cases
Nov 23, 2012 · The tumor types consisted of carcinoma (58%), melanoma (22%) and sarcoma (20%). Ovary was the most common site of origin for carcinoma, and ...
[46]
Axillary lymph node metastases from unknown primary
Axillary cancers from an unknown primary (CUPax) are defined as isolated metastatic axillary lymphadenopathy without an established primary site [1]. Aside from ...
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Isolated Contralateral Axillary Lymph Node Involvement in Breast ...
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Contralateral axillary lymph node metastasis in breast cancer
Oct 7, 2023 · Contralateral axillary lymph node metastasis (CAM) is rare. It remains controversial whether CAM should be regarded as a regional or distant ...
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Axillary Lymphadenopathy - Radiology - UCLA Health
Malignant cases of axillary lymphadenopathy include lymphoma/leukemia and metastatic disease. Bilateral and symmetric lymph node abnormalities are ...
[50]
Locally advanced breast cancer arising in the axilla - PMC - NIH
Sep 19, 2022 · Breast cancer can arise from this ectopic tissue, most commonly in the axilla (60–70% of cases) and is of similar type to orthotopic breast ...
[51]
Axillary Primary and Breast Cancer Management
Jan 23, 2021 · Axillary primary breast cancer, also known as occult primary breast cancer, is a rare entity representing less than 1% of all breast cancers.
[52]
Primary Mucinous Adenocarcinoma of Skin in Axilla: A Case Report ...
PMCS is an uncommon subtype of sweat gland tumor, with <150 cases described in the literature till date.[1,2] It is usually seen in the head and neck region, ...
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A Rare Primary Cutaneous Myoepithelial Carcinoma in the Axilla ...
Nov 12, 2024 · Primary cutaneous myoepithelial carcinoma is an extremely rare tumor, and to the best of our knowledge, it has never been reported to occur ...
[54]
Axillary node metastases with occult primary breast cancer - UpToDate
Dec 17, 2024 · INTRODUCTION. Cancer of unknown primary site (CUP), defined as the presence of metastatic cancer with an undetectable primary site at the ...
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Axillary Nodal Metastases from Carcinoma of Unknown Primary ...
May 25, 2021 · The most common cause of metastatic axillary lymph nodes is ipsilateral breast cancer. However, other adenocarcinomas can metastasize to the ...
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View of Axillary Lymph Node Dissection in Breast Cancer
However,clinical evaluation of axillary lymph nodes can be highlyinaccurate. Up to 67% of nodes thought to be diseased ona clinical basis have been found to be ...
[57]
Patterns of axillary nodal involvement in breast cancer. Predictability ...
The purpose was to determine the accuracy of level one axillary dissection in predicting the status of the entire lymph node chain in carcinoma of the breast.
[58]
Axillary Lymphadenectomy - StatPearls - NCBI Bookshelf - NIH
Axillary lymphadenectomy, or axillary dissection, is a surgical procedure involving the removal of all lymphatic tissue from the axilla.
[59]
Axillary Dissection: Overview, Periprocedural Care, Technique
Oct 17, 2024 · Axillary dissection is a surgical procedure that incises the axilla to identify, examine, or remove lymph nodes.
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Breast Cancer and Axillary Lymph Node Dissection - Breastcancer.org
Jul 30, 2025 · An axillary lymph node dissection removes lymph nodes from under the arm to see if the cancer has moved beyond the breast.
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Axillary Sentinel Lymph Node Biopsy - StatPearls - NCBI Bookshelf
Jul 3, 2023 · Sentinel lymph node biopsy was developed to allow for assessment of the axillary lymph node status without a formal axillary dissection.Continuing Education Activity · Introduction · Anatomy and Physiology · Indications
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Sentinel Lymph Node Biopsy - NCI - National Cancer Institute
Jun 25, 2019 · A sentinel lymph node biopsy (SLNB) is a procedure in which the sentinel lymph node is identified, removed, and examined to determine whether cancer cells are ...What are lymph nodes? · What is a sentinel lymph node...
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Technique of axillary lymph node dissection - UpToDate
Jun 26, 2024 · Evaluation of the axilla provides information for treatment decisions in patients with invasive breast cancer. Axillary lymph node ...
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Peripheral Matters | Axillary Artery: Alternate Access for Large Bore ...
Jun 22, 2018 · The axillary artery has emerged as a feasible and safe alternative access for delivering large bore sheaths in TAVR or MCS.<|separator|>
[65]
SCAI Position Statement on Best Practices for Percutaneous Axillary ...
Apr 19, 2022 · This statement aims to review the anatomic considerations and risks for percutaneous axillary artery access, suggest best practices for access techniques.
[66]
Botulinum toxin A for axillary hyperhidrosis (excessive sweating)
Botulinum toxin A can stop excessive sweating by blocking the release of acetylcholine, which mediates sympathetic neurotransmission in the sweat glands.
[67]
Low-Dose Efficacy of Botulinum Toxin A for Axillary Hyperhidrosis
Short- and long-term results show that doses of 100 and 200 U of botulinum toxin A are equally safe and effective.
[68]
Chapter 83. Biology of Eccrine and Apocrine Glands - AccessMedicine
2 Analgen of eccrine sweat glands first appear in the 3.5-month-old fetus on the palms and soles (see Chapter 7), then develop in the axillary skin in the fifth ...<|separator|>
[69]
A short history of sweat gland biology - Wilke - Wiley Online Library
May 23, 2007 · Apoeccrine glands, which contribute notably to axillary secretion by emitting high amounts of watery fluid, show strong cholinergic sensitivity ...Introduction · Eccrine Sweat Glands · Apocrine Sweat Glands
[70]
Human Pheromones - Neurobiology of Chemical Communication
Most proponents of the human pheromone concept assume that skin glands are the source of the active pheromonal agents. All three major skin glands—apocrine ...
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Pheromones and their effect on women's mood and sexuality - NIH
Some data indicate that 16-androstene pheromones, in particular androstadienone, play a beneficial role in women's mood, focus and sexual response.Missing: hypotheses | Show results with:hypotheses
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https://www.researchgate.net/publication/10883805_Male_Axillary_Extracts_Contain_Pheromones_that_Affect_Pulsatile_Secretion_of_Luteinizing_Hormone_and_Mood_in_Women_Recipients
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Pheromones in sex and reproduction: Do they have a role in humans?
Pheromones are chemical messengers that may affect human behavior and reproduction, with studies supporting their role, though weak. They are chemical ...
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The search for human pheromones: the lost decades and ... - Journals
Apr 7, 2015 · There is no robust evidence for current claims of human pheromones. The search needs to return to first principles, using rigorous methods and ...2. Pheromones Are Chemical... · (a) Androstenone And... · (b) Androstadienone And...
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Facts, fallacies, fears, and frustrations with human pheromones
Oct 7, 2004 · Sufficient evidence, much still accumulating, suggests the presence of four types of pheromones in human chemical communication. These include ...Missing: hypotheses | Show results with:hypotheses
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Human pheromones and sexual attraction - ScienceDirect.com
In this article we review the present evidence of the effect of human pheromones and discuss the role of olfactory cues in human sexual behaviour.
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Androgens and hair growth - PubMed
Normally around puberty, androgens stimulate axillary and pubic hair in both sexes, plus the beard, etc. in men, while later they may also inhibit scalp hair ...
[78]
Premature Adrenarche - Cleveland Clinic
May 3, 2024 · Pubic and armpit (axillary) hair: Pubic hair is darker and thicker body hair that grows in your genital region. Androgens stimulate the growth ...
[79]
Androgen-dependent human hair growth: a biological paradox
Androgens are the main regulator of changes in human hair growth. They stimulate the production of pigmented terminal hair in many areas after puberty.
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Microbial Origins of Body Odor | Lacy Lab
Feb 23, 2022 · Apocrine glands produce an odorless fluid composed of proteins, lipids, fatty acids, branched-chain amino acids, vitamins, and steroids (i.e., ...
[81]
Mapping axillary microbiota responsible for body odours using a ...
Jan 24, 2015 · Human axillary odour is commonly attributed to the bacterial degradation of precursors in sweat secretions. To assess the role of bacterial ...
[82]
Intrinsic and extrinsic factors affecting axillary odor variation. A ...
Oct 15, 2023 · This article focuses on the biological mechanisms underlying the creation of axillary odor, as well as the intrinsic and extrinsic factors likely to impact the ...
[83]
A comparative clinical study of different hair removal procedures and ...
Dec 10, 2015 · Axillary hair can influence the development of underarm odor in men. To compare different hair removal procedures and their impact on the ...
[84]
Shaving of axillary hair has only a transient effect on perceived body ...
Aug 7, 2025 · Odors of the shaved armpits were rated more pleasant, attractive, and less intense compared to the unshaved armpits.
[85]
Men's Shaved Armpits Smell Better to Women, by a Hair - NBC News
Jan 5, 2012 · The study's female participants found the smell of freshly shaven pits more pleasant than pits that had been growing hair for six to 10 weeks.Local · Tv · Featured<|separator|>
[86]
The human axillary organ: An evolutionary puzzle | Human Evolution
The axillary organ took on a new role, namely to provide odorous stimulation for strengthening the pairbond, and lost its previous role as advertiser of ...
[87]
Why Do We Have Armpit Hair? And Other Body Hair Answers
Feb 28, 2020 · A 2016 studyTrusted Source involving men found that removing armpit hair by shaving significantly reduced axillary odor for the following 24 ...
[88]
Does shaving your armpits reduce sweating? - Health | HowStuffWorks
May 9, 2014 · Underarm hair can trap moisture, too, creating a swampy environment that odor-causing bacteria revel in. So you may feel dryer (and therefore ...
[89]
Does Shaving Armpits Reduce Sweat? - Truly Beauty
Jan 15, 2024 · Technically, no. Shaving your armpits will not reduce sweat but it can make you feel more comfortable and reduce the appearance of sweat stains.
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https://getbevel.com/blogs/articles/armpit-grooming-101-the-dos-and-donts
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https://sexysmoothwax.com/blogs/news/the-evolution-of-body-hair-a-journey-through-time-and-culture
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[PDF] Why Are We Grossed Out by Women With Pit Hair?
Jun 26, 2014 · In Leviticus, a complete body shave is mandated in the treatment of leprosy. So, humans have a long history of being disgusted at armpit hair ...
[93]
Hair Removal | Smithsonian Institution
In the 1920s, the new fashion for sleeveless tops and short dresses meant that the legs and armpits of American women were now visible in social situations, ...
[94]
Why did body odor start grossing us out? | National Geographic
Jun 28, 2024 · First, grooming habits became a way for the elite to enforce their status. As bathing became widely available, new standards of scent made for lucrative ...Missing: cross- | Show results with:cross-<|separator|>
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Why many East Asians don't have body odor or need deodorant
Jun 21, 2024 · Between 80 and 95% of East Asians have a dysfunction of the ABCCII gene, which is linked to smelly pits, a number of studies say.Missing: attitudes | Show results with:attitudes
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Female body hair!. In France (for example), underarm hair…
Apr 5, 2019 · In France (for example), underarm hair is considered a normal (perhaps even complementary) component of natural body odor.
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Humans and the Olfactory Environment: A Case of Gene-Culture ...
For example, a cross-cultural study found that Japanese participants tended to rate “Japanese” odors as more intense, while German participants tended to rate “ ...
[98]
The neurobiology of ticklishness - ScienceDirect.com
Gargalesis tends to be concentrated on areas such as the feet, armpits, torso, and stomach, whereas knismesis is reported across more broadly distributed body ...Missing: axilla | Show results with:axilla
[99]
Why Can't You Tickle Yourself? - Britannica
Oct 9, 2025 · Ticklishness can occur in many places on the body, but the most common are the ribcage, the armpit, and the sole of the foot.
[100]
The human tickle response and mechanisms of self-tickle suppression
Sep 21, 2022 · Our data show that physiological responses to tickling occur within half a second after tickle onset, considerably faster than previously ...
[101]
The extraordinary enigma of ordinary tickle behavior - PubMed Central
May 23, 2025 · Early animal and human physiological work suggested that ticklish sensations are detected by C low-threshold mechanoreceptive free nerve endings ...
[102]
Why Are People Ticklish? - Cleveland Clinic Health Essentials
May 30, 2024 · Tickling stimulates your hypothalamus, which controls your body's fight-or-flight response when it senses danger. Why the laughter?