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Atopy

Atopy is a hereditary predisposition to develop immunoglobulin E (IgE)-mediated hypersensitivity reactions to common environmental allergens, leading to a range of allergic conditions including allergic rhinitis, asthma, and atopic dermatitis.^[1] The term, derived from the Greek word atopia meaning "out of place," was coined in 1923 by American allergists Arthur F. Coca and Robert A. Cooke to describe inherited tendencies toward immediate hypersensitivity reactions distinct from other forms of allergy.^[2] This predisposition arises from a complex interplay of genetic and environmental factors, with key genetic influences including mutations in the filaggrin gene that impair skin barrier function and promote allergen penetration.^[3] Atopy drives a Th2-biased immune response, characterized by overproduction of IgE antibodies, eosinophil activation, and cytokine release such as interleukin-4 and interleukin-13, which amplify allergic inflammation.^[1] Clinically, it manifests as the "atopic march," a progressive sequence where early-onset atopic dermatitis in infancy often precedes allergic rhinitis in childhood and asthma in adolescence or adulthood. Globally, atopy affects 10% to 30% of individuals in developed countries,^[1] with rising prevalence attributed to urbanization, hygiene practices, and dietary changes that alter microbial exposure during critical developmental windows.^[4] In children, the lifetime prevalence of atopic diseases can reach 20% or higher in industrialized regions, though rates vary by geography—lower in rural or low-income settings but increasing rapidly in emerging economies.^[5] Management focuses on allergen avoidance, pharmacotherapy like antihistamines and topical corticosteroids, and emerging biologics targeting IgE or Th2 pathways, underscoring atopy's role as a foundational driver of allergic morbidity worldwide.^[1]

Definition and Overview

Definition

Atopy is defined as a hereditary predisposition to develop immunoglobulin E (IgE)-mediated hypersensitivity reactions to common environmental allergens, such as pollen, dust mites, and pet dander.^[6] This genetic tendency results in an exaggerated immune response characterized by the production of specific IgE antibodies against otherwise harmless substances, distinguishing it from non-IgE-mediated allergies.^[7] The term "atopy" was coined in 1923 by allergists Arthur F. Coca and Robert Cooke to describe familial tendencies toward certain allergic conditions, emphasizing their inherited nature and separation from infectious or toxic hypersensitivities.^[8] A hallmark of atopy is the "atopic march," which refers to the typical sequential progression of allergic manifestations beginning with atopic dermatitis in infancy, followed by allergic rhinitis in early childhood, and often culminating in asthma during later childhood or adolescence.^[9] This progression reflects the underlying predisposition and is observed in a significant proportion of affected individuals, though not all follow the exact sequence.^[10] Key characteristics of atopy include an exaggerated T helper 2 (Th2) immune response, which promotes IgE class switching and eosinophil activation; persistently elevated total serum IgE levels; and positive skin prick tests to common aeroallergens or food allergens, indicating sensitization.^[11]^[7] These features underpin the predisposition to conditions such as asthma and eczema.^[12]

Associated Conditions

Atopy is primarily manifested through the core atopic triad of atopic dermatitis (eczema), allergic rhinitis (hay fever), and asthma, which share underlying IgE-mediated hypersensitivity mechanisms and often present sequentially or concurrently in affected individuals.^[1]^[13] These conditions exemplify the interconnected nature of atopic disorders, where early-onset atopic dermatitis frequently precedes the development of respiratory allergies like allergic rhinitis and asthma in a progression termed the atopic march.^[2] Beyond the triad, atopy is associated with other allergic conditions, including food allergies, urticaria, and eosinophilic esophagitis, which arise from similar dysregulated immune responses to environmental triggers.^[14]^[15] Food allergies, in particular, often co-occur with atopic dermatitis and can exacerbate the overall atopic burden.^[16] Co-occurrence among atopic conditions is notably high, with studies showing that up to 60% of children with severe atopic dermatitis progress to asthma, and children with atopic dermatitis face a sixfold increased risk of developing food allergies compared to non-atopic peers.^[2] Additionally, up to 75% of individuals with asthma exhibit concomitant allergic rhinitis symptoms, underscoring the multimorbid profile of atopy.^[2] A key feature of atopy is polysensitization, wherein affected individuals develop IgE-mediated reactivity to multiple allergen categories, such as aeroallergens (e.g., pollen and dust mites) and foods, heightening the risk of diverse allergic manifestations across organ systems.^[17] This phenomenon contributes to the observed clustering of conditions and emphasizes the systemic predisposition in atopic individuals.^[17]

Clinical Presentation

Signs and Symptoms

Atopic conditions, which encompass a predisposition to allergic hypersensitivity, commonly manifest with intense pruritus (itching) as a hallmark symptom, often leading to recurrent exacerbations that flare in response to triggers such as allergens or irritants.^[1] Patients frequently report a personal or family history of atopy, reflecting the hereditary nature of these disorders, though this is more indicative of underlying susceptibility than an acute sign.^[18] These symptoms vary by the specific atopic disease but share a pattern of chronic inflammation affecting the skin, respiratory tract, or both. In atopic dermatitis, the primary presentation involves dry, eczematous rashes that appear as red, inflamed patches, particularly on the face, flexures, and extremities in infants and children, accompanied by severe itching that worsens at night.^[19] Allergic asthma typically features wheezing, shortness of breath, cough (often nocturnal), and chest tightness, which may be episodic and triggered by exposure to allergens like pollen or dust mites.^[20] Allergic rhinitis, meanwhile, is marked by sneezing, clear rhinorrhea, nasal congestion, and itchy eyes or throat, with symptoms peaking seasonally or perennially depending on allergen exposure.^[21] The atopic march describes a common progression where symptoms often begin with skin involvement in early childhood, such as atopic dermatitis in infancy, followed by the development of food allergies, asthma, and allergic rhinitis in later years, with studies showing that approximately one-third develop asthma, about 35% develop food allergies, and up to 45% develop allergic rhinitis.^[9]^[22] However, the atopic march is not observed in all cases, and its existence as a linear progression remains a topic of ongoing research and debate.^[22] This sequential pattern underscores the interconnected nature of atopic manifestations. Complications arising from these symptoms include sleep disturbances due to unrelenting pruritus or nocturnal wheezing, which can impair daily functioning and growth in children.^[23] Secondary bacterial infections, such as those from Staphylococcus aureus, frequently occur from scratching-induced skin breakdown in atopic dermatitis.^[19] Overall, these conditions substantially reduce quality of life, contributing to psychological distress, social limitations, and decreased productivity across all ages.^[18]

Diagnosis

Diagnosis of atopy relies primarily on a thorough clinical history that identifies a personal or family history of atopic diseases, such as asthma, allergic rhinitis, or atopic dermatitis, along with IgE-mediated symptoms triggered by common environmental allergens like pollen, house dust mites, or animal dander.^[1]^[24] This history helps establish the genetic predisposition and pattern of immediate hypersensitivity reactions characteristic of atopy.^[25] Laboratory evaluations support the clinical assessment through measurement of total serum IgE levels, which are frequently elevated in atopic individuals, reflecting heightened IgE production.^[25] Allergen-specific IgE testing, performed via radioallergosorbent test (RAST) or ImmunoCAP assays, detects sensitization to particular allergens by quantifying IgE antibodies in serum, with levels above 0.35 kUA/L typically indicating positivity.^[26] Peripheral blood eosinophil counts are also assessed, as eosinophilia often accompanies atopic conditions due to allergic inflammation.^[27] Skin prick testing serves as a frontline in vivo method for confirming IgE-mediated sensitization, involving the application of standardized allergen extracts to the volar forearm or back, followed by a gentle prick or puncture with a lancet to introduce the allergen into the epidermis.^[28] After 15-20 minutes, the response is interpreted by measuring the wheal (indurated area) diameter; a wheal greater than 3 mm larger than the negative control is generally considered positive, indicating clinical relevance when correlated with history. Limitations include potential false-positive reactions in patients with dermographism, where non-specific skin reactivity mimics allergic responses, necessitating careful interpretation and sometimes antihistamine withdrawal prior to testing.^[28]^[29] Emerging diagnostic tools enhance precision in identifying atopy. Component-resolved diagnostics (CRD) employs recombinant or purified allergen components to measure IgE reactivity to specific molecular epitopes, enabling differentiation between true allergies and cross-reactivities for more targeted management.^[30]^[31] Genetic testing for loss-of-function mutations in the filaggrin (FLG) gene identifies individuals at higher risk for atopic dermatitis by detecting impaired skin barrier function, though it is not routinely used for all cases but rather in severe or familial presentations.^[32]^[33] Differential diagnosis involves ruling out non-IgE-mediated conditions to confirm atopic etiology, such as irritant contact dermatitis, which presents with similar eczematous lesions but lacks allergen-specific IgE and history of atopy, or intrinsic asthma, characterized by airway inflammation without demonstrable sensitization to airborne allergens.^[24]^[34] These distinctions are guided by the absence of positive skin prick or specific IgE tests in non-atopic mimics.

Pathophysiology

Immune Mechanisms

Atopy is characterized by a type I hypersensitivity reaction, an immediate IgE-mediated immune response triggered by allergen exposure in sensitized individuals. Upon re-exposure to the allergen, IgE antibodies bound to high-affinity FcεRI receptors on mast cells and basophils cross-link, leading to rapid degranulation and release of preformed mediators such as histamine, as well as newly synthesized lipid mediators like leukotrienes and prostaglandins, and cytokines including TNF-α.^[35]^[36] This cascade initiates acute symptoms like vasodilation, increased vascular permeability, and smooth muscle contraction, while also promoting chronic inflammation through recruitment of additional immune cells.^[37] Central to atopic immune responses is the differentiation of CD4+ T helper cells into Th2 cells, predominantly driven by cytokines IL-4 and IL-13 produced by innate lymphoid cells type 2 (ILC2s) and early Th2 cells. IL-4 signals through the IL-4Rα/γc receptor complex, activating STAT6 to promote Th2 lineage commitment from naïve T cells, while both IL-4 and IL-13 induce B-cell class switching to IgE production via similar STAT6-dependent pathways in germinal centers.^[38]^[39] This Th2 bias amplifies IgE synthesis and sustains allergic inflammation, with IL-13 further contributing to tissue remodeling and mucus hypersecretion in affected sites.^[40] Impaired function of regulatory T cells (Tregs), particularly Foxp3+ CD4+ Tregs, impairs suppression of Th2 responses in atopic individuals, leading to unchecked allergic inflammation. Tregs normally inhibit Th2 cell proliferation and cytokine production through mechanisms like CTLA-4-mediated suppression of antigen-presenting cells and secretion of anti-inflammatory cytokines such as IL-10 and TGF-β; however, reduced Treg numbers or function in atopics fails to restore immune tolerance to harmless allergens.^[41]^[42] This imbalance is evident in lesional skin and airways, where diminished Treg activity correlates with exacerbated Th2-driven pathology.^[43] Epigenetic modifications, particularly DNA methylation changes, contribute to the Th2-biased immune profile in atopy by altering gene expression in immune cells. Hypermethylation of Th1-associated loci and hypomethylation of Th2 genes in T cells and B cells promote sustained Th2 differentiation and IgE class switching, often established early in life or influenced by environmental exposures.^[44]^[45] These stable epigenetic marks, including histone modifications, reinforce the atopic phenotype across generations and tissues.^[46] Key cytokines and immune cells further orchestrate atopic responses: IL-5, secreted by Th2 cells and ILC2s, drives eosinophil maturation, survival, and activation in bone marrow and tissues, amplifying tissue eosinophilia and damage through release of cytotoxic granule proteins like major basic protein.^[47]^[48] Basophils, activated via IgE cross-linking, serve as rapid sources of IL-4 and IL-13, enhancing Th2 polarization and recruiting other effectors early in allergic reactions.^[49] Dendritic cells, particularly those expressing CD1a in the skin, present allergens to naïve T cells via MHC II and co-stimulatory molecules, priming Th2 differentiation through production of IL-4-inducing factors like TSLP and OX40L.^[50] These interactions, while influenced by barrier defects that facilitate allergen entry, underscore the core immunological dysregulation in atopy.^[51]

Barrier Dysfunction

Barrier dysfunction in atopy refers to structural defects in epithelial tissues that compromise their protective role, allowing environmental allergens and irritants to penetrate more easily and initiate or sustain allergic responses. In the skin, mutations in the filaggrin gene (FLG) represent a key genetic predisposition to impaired barrier integrity, resulting in reduced filaggrin protein expression that disrupts the stratum corneum's lipid matrix and desquamation process.^[52] This leads to increased transepidermal water loss (TEWL), a hallmark of dry and vulnerable skin in atopic dermatitis, where TEWL levels are often elevated even in non-lesional areas compared to healthy controls.^[53] Non-invasive assessments, such as TEWL measurement using evaporimeters and corneometry to quantify stratum corneum hydration, provide objective quantification of these defects and correlate with disease severity.^[54] In respiratory and mucosal barriers, atopy involves diminished expression of tight junction proteins, including claudins (e.g., claudin-1 and claudin-7) and occludins, which seal intercellular spaces in airway and nasal epithelia.^[55] These reductions, observed in conditions like asthma and allergic rhinitis, increase epithelial permeability, enabling allergens to access subepithelial immune cells and trigger sensitization.^[56] Consequences of such barrier impairments across epithelial sites include heightened allergen sensitization through direct antigen presentation to dendritic cells, predisposition to microbial superinfections due to easier pathogen ingress (e.g., Staphylococcus aureus colonization in atopic skin), and perpetuation of chronic inflammation via sustained exposure to triggers.^[57]^[58]^[59] This interplay forms a vicious cycle, wherein initial barrier defects promote inflammation that further degrades epithelial integrity, thereby maintaining the atopic state over time. Th2 cytokines, such as IL-4 and IL-13, contribute to this by downregulating tight junction proteins and filaggrin expression.^[60]

Etiology

Genetic Factors

Atopy, characterized by an exaggerated IgE-mediated immune response to common allergens, exhibits a strong genetic basis through polygenic inheritance, where multiple genes each contribute small effects to disease susceptibility. Heritability estimates for atopic traits, including atopic dermatitis (AD), asthma, and allergic rhinitis, range from 50% to 80%, derived from family and twin studies that highlight the substantial genetic influence on disease development.^[61]^[62] Family studies, particularly twin concordance analyses, provide robust evidence for this genetic predisposition. Monozygotic twins show significantly higher concordance rates for atopic conditions compared to dizygotic twins; for instance, pairwise concordance for AD reaches 0.72 in monozygotic pairs versus 0.23 in dizygotic pairs, underscoring the role of shared genetics over environmental factors alone.^[63] Similar patterns hold for asthma and other atopic diseases, with monozygotic concordance typically ranging from 20% to 50% in population-based cohorts.^[64] Among key genes implicated in atopy, loss-of-function mutations in the filaggrin gene (FLG) on chromosome 1q21 represent the strongest risk factor for impaired skin barrier function, predisposing individuals to AD and secondary allergic sensitization. Cytokine-related genes such as IL4 and IL13 on chromosome 5q31 promote Th2 immune skewing and IgE production, enhancing susceptibility to allergic inflammation across atopic disorders. Additionally, ADAM33 on chromosome 20p13 contributes to airway remodeling in asthma, influencing bronchial hyperresponsiveness through its role in metalloproteinase activity.^[61]^[65]^[66] Genome-wide association studies (GWAS) have further delineated these polygenic contributions, identifying susceptibility loci such as the 17q21 region harboring ORMDL3, which regulates sphingolipid biosynthesis and is strongly linked to childhood-onset asthma. The seminal GWAS by Moffatt et al. (2007) demonstrated that variants near ORMDL3 increase asthma risk by upregulating gene expression in airway epithelial cells, with odds ratios up to 1.5 in pediatric cohorts. These findings have been replicated across diverse populations, confirming the locus's role in early-life atopy. Epistatic interactions, including gene-environment effects, modulate atopic risk; for example, FLG mutations exacerbate skin barrier dysfunction and AD severity in low-humidity environments, where reduced moisture impairs filaggrin processing and increases transepidermal water loss. Such interactions highlight how genetic variants interact with external conditions to influence disease penetrance.^[67]^[68]

Environmental Triggers

Environmental triggers play a pivotal role in provoking or exacerbating atopy by interacting with genetic predispositions, leading to sensitization and immune dysregulation in susceptible individuals.^[69] Among these, common allergens act as primary sensitizers, initiating IgE-mediated responses that underpin atopic conditions such as asthma, allergic rhinitis, and atopic dermatitis. House dust mites (HDM), particularly species like Dermatophagoides pteronyssinus and D. farinae, are ubiquitous indoor allergens whose fecal pellets and body fragments contain potent proteins (e.g., Der p 1 and Der f 1) that penetrate airway and skin barriers, promoting Th2-skewed inflammation and sensitization in early life.^[70] Pollen from trees (e.g., birch), grasses (e.g., timothy), and weeds (e.g., ragweed) serves as a key outdoor allergen, triggering seasonal exacerbations of allergic rhinitis and asthma through inhalation and mucosal exposure, with sensitization rates varying by geographic region and exposure intensity.^[69] Pet dander from cats (Fel d 1) and dogs (Can f 1) represents another major indoor sensitizer, with proteins adhering to household surfaces and persisting in environments, increasing the risk of perennial allergic symptoms in atopic children and adults.^[69] Food allergens, such as peanuts (Ara h 1–3), exemplify ingested sensitizers that can provoke systemic reactions; early environmental exposure via skin or airway routes, as in household dust, heightens the likelihood of peanut allergy in those with impaired barriers.^[71] Irritants and pollutants further aggravate atopy by directly damaging epithelial barriers and amplifying inflammatory responses, particularly in the airways. Tobacco smoke, both active and secondhand, contains over 4,000 chemicals that irritate mucous membranes, significantly increasing the risk of asthma by 20% to 85% in exposed children through enhanced bronchial hyperresponsiveness and reduced lung function.^[72] Air pollution, including fine particulate matter (PM2.5) from vehicle emissions and industrial sources, penetrates deep into the lungs, promoting oxidative stress and Th2 cytokine production, with long-term exposure linked to a 30% attributable fraction of asthma cases in urban populations.^[73] Occupational exposures to irritants like diisocyanates in manufacturing or latex in healthcare settings constitute a significant risk, accounting for 5–15% of adult asthma cases and often leading to work-exacerbated atopy through repeated inhalation and sensitization.^[74] Microbiome dysbiosis emerges as a critical environmental factor, where reduced early-life exposure to diverse microbes disrupts immune tolerance and fosters atopic predisposition. The hygiene hypothesis posits that diminished contact with commensal bacteria due to modern sanitation, antibiotic use, and urban living impairs the development of regulatory T cells, elevating atopy risk in low-exposure cohorts.^[75] Early-life factors such as cesarean delivery or formula feeding alter gut microbiota composition, reducing diversity (e.g., lower Bifidobacterium levels) and correlating with subsequent asthma and eczema onset, as evidenced in prospective birth cohorts.^[75] In atopic dermatitis, colonization by Staphylococcus aureus exacerbates disease through toxin-mediated mechanisms that amplify Th2-driven inflammation. This bacterium, prevalent on 60–100% of lesional skin in affected patients, produces superantigens like staphylococcal enterotoxin B (SEB) and toxic shock syndrome toxin-1 (TSST-1), which bypass normal antigen presentation to polyclonally activate T cells, boosting IL-4 and IL-13 production while suppressing antimicrobial peptides.^[76] These superantigens also induce IgE-specific responses against self-superantigens, perpetuating a cycle of barrier breakdown and chronic inflammation in atopic skin. Emerging climate and lifestyle factors contribute to atopy by modulating immune homeostasis and barrier integrity. Urbanization correlates with higher atopic disease prevalence, attributed to increased pollutant exposure and reduced microbial diversity compared to rural settings, with urban children showing 1.5–2 times greater risk of asthma and eczema.^[77] Vitamin D deficiency, often stemming from limited sunlight in urban or indoor lifestyles, impairs antimicrobial defense and Th2 regulation, associating with worsened atopic dermatitis severity in up to 80% of deficient pediatric cases.^[77] Diets low in omega-3 polyunsaturated fatty acids (e.g., from fish), common in Western patterns, promote pro-inflammatory eicosanoids, elevating atopic risk; maternal omega-3 supplementation during pregnancy reduces offspring eczema incidence by 20–30%.^[77]

Epidemiology

Prevalence Patterns

Atopy, characterized by a hereditary predisposition to produce immunoglobulin E (IgE) antibodies in response to common allergens, affects an estimated 10-30% of the population in developed countries.^[1] This encompasses a range of allergic conditions, including atopic dermatitis, which has a prevalence of 10-20% among children worldwide.^[78] The burden is particularly notable in pediatric populations, where atopic sensitization—evidenced by positive skin prick tests or elevated specific IgE—manifests early and influences the development of multiple allergic phenotypes.^[79] Demographic patterns reveal variations by sex, with allergic rhinitis showing a higher prevalence in females, especially post-puberty, due to hormonal influences on immune responses.^[80] Socioeconomic disparities may play a role, though findings are mixed and vary by region and access to healthcare.^[81] Age distribution demonstrates a peak in childhood, where asthma prevalence reaches 10-20% in individuals under 18 years, reflecting the early onset of atopic manifestations.^[82] Many cases of asthma show partial resolution during adolescence, with symptoms diminishing in 30-70% of affected youth as immune maturation occurs.^[83] For atopic dermatitis, remission occurs in approximately 40-70% by school age or adolescence.^[84] Regional variations highlight higher prevalence in developed countries, such as Australia where up to 40% of children exhibit atopic sensitization.^[85] In contrast, developing regions report lower rates, though these are rising in urbanizing areas. Approximately 50% of individuals with atopy experience multiple comorbid conditions, including combinations of asthma, rhinitis, and dermatitis, amplifying overall disease burden.^[86] Increasing trends in prevalence have been linked to lifestyle changes, such as urbanization and dietary shifts.^[87]

Trends Over Time

Since the 1970s, the prevalence of atopic diseases has risen substantially in Western countries, often doubling or more over several decades.^[4] For instance, in the United Kingdom, the prevalence of reported wheeze among children increased from approximately 9.8% in 1973 to 19.7% by 2003, reflecting a near doubling that aligns with broader trends in childhood asthma and atopy.^[88] This escalation has been attributed to lifestyle and environmental shifts in industrialized settings, contributing to a global recognition of atopy as an emerging public health concern.^[89] Following the onset of the COVID-19 pandemic in 2020, trends in high-income countries showed signs of stabilization or slight declines in atopic disease prevalence, particularly during lockdowns. Reduced air pollution and limited exposure to respiratory infections were key factors, as lockdowns curtailed outdoor activities and urban emissions in regions like South Korea and parts of Europe.^[90] For example, atopic dermatitis prevalence among Korean adolescents declined notably post-2020, with studies linking this to decreased environmental triggers.^[91] These temporary shifts highlight the role of modifiable exposures in modulating atopy rates, though long-term stabilization remains under investigation.^[92] As of 2021, global atopic dermatitis cases reached 129 million, with projections indicating continued increases in low- and middle-income countries by mid-century.^[93] Several hypotheses explain these temporal patterns. The hygiene hypothesis posits that diminished early-life exposure to microbes in sanitized, urban environments promotes a Th2-skewed immune response, favoring allergic sensitization over tolerance.^[4] This theory, supported by lower atopy rates in less hygienic settings, suggests that reduced microbial diversity impairs regulatory T-cell development and immune balance.^[94] Complementing this, the dual allergen exposure hypothesis differentiates routes of allergen contact: high-dose oral exposure in early infancy induces tolerance, while low-dose cutaneous exposure through compromised skin barriers leads to sensitization and atopy.^[95] Additionally, shifts toward Western diets—characterized by high processed food intake and low fiber—have been linked to rising atopy, as they alter gut microbiota and exacerbate inflammatory Th2 pathways.^[96] Looking ahead, atopy prevalence is projected to continue increasing in low- and middle-income countries, driven by rapid urbanization that mirrors Western lifestyle changes. Urban migration exposes populations to higher pollutant levels, dietary shifts, and reduced microbial diversity, potentially elevating rates of asthma and atopic dermatitis by mid-century.^[97] These trends underscore the need for targeted monitoring in transitioning economies to mitigate future burdens.^[98]

Management

Prevention Strategies

Primary prevention strategies for atopic diseases focus on interventions during pregnancy and early infancy to reduce the risk of onset in genetically susceptible individuals. Exclusive breastfeeding for at least 4 to 6 months is recommended, as it has been associated with a reduced incidence of atopic dermatitis in children under 2 years and early wheezing under 4 years.^[99] Maternal avoidance of common allergens such as cow's milk, eggs, or peanuts during pregnancy or lactation is not advised, as systematic reviews indicate it does not significantly lower the risk of atopic eczema or other atopic conditions in offspring and may pose nutritional risks to the mother and fetus.^[100] Early supplementation with probiotics, particularly strains like Lactobacillus rhamnosus, shows potential in reducing the incidence of atopic dermatitis, with meta-analyses reporting a statistically significant preventive effect when administered to mothers during pregnancy and to infants postnatally.^[101] For high-risk infants—those with severe eczema or egg allergy—early introduction of peanuts between 4 and 11 months of age, as demonstrated by the Learning Early About Peanut Allergy (LEAP) study, substantially lowers the risk of developing peanut allergy, with an 81% relative reduction observed compared to avoidance.^[102] Environmental controls in the home environment are also emphasized to minimize early exposures. Avoiding tobacco smoke exposure is critical, as secondhand smoke during pregnancy and infancy increases the odds of atopic dermatitis and other allergic sensitization.^[103] Measures to reduce indoor allergens, such as using mite-proof bedding covers to limit house dust mite exposure, are commonly recommended, though randomized trials indicate they do not significantly decrease the primary incidence of atopic dermatitis.^[104] Public health measures play a role in broader prevention by addressing modifiable environmental factors that exacerbate atopic trends. Regulations to reduce air pollution, including fine particulate matter and nitrogen dioxide, could prevent a substantial proportion of atopic dermatitis cases, with estimates suggesting up to 16% of late-life eczema attributable to poor air quality in high-pollution areas.^[105] Vaccination programs, such as those involving bacille Calmette-Guérin (BCG) in early childhood, have been linked to a lower risk of atopic diseases in developed countries, potentially by modulating immune responses.^[106] Secondary prevention targets infants already showing signs of atopy to interrupt the "atopic march" toward more severe manifestations like asthma or allergic rhinitis. Proactive use of moisturizers from birth in high-risk infants supports skin barrier function; a randomized controlled trial showed a reduction in the incidence of atopic dermatitis by approximately 50% during the application period, though meta-analyses indicate more modest effects (~36% up to 6 months) and long-term effects on the full atopic march require further study.^[107]^[108] Guidelines from organizations like the American Academy of Allergy, Asthma & Immunology (AAAAI) recommend screening families with a history of atopy—such as asthma, allergic rhinitis, or atopic dermatitis in parents or siblings—to identify infants at elevated risk for food allergies and other atopic conditions, prompting targeted interventions like early allergen introduction.

Treatment Options

Treatment of atopic conditions primarily involves a stepwise approach tailored to the specific manifestation—such as atopic dermatitis, asthma, or allergic rhinitis—and disease severity, focusing on symptom control and quality of life improvement. Updated 2024-2025 guidelines from the American Academy of Dermatology (AAD) and AAAAI emphasize personalized stepwise management, incorporating recent approvals for additional Janus kinase inhibitors and biologics.^[109]^[110] Allergen avoidance forms the cornerstone of initial management, emphasizing environmental modifications to reduce exposure to triggers like dust mites, pet dander, and pollen. Strategies include using high-efficiency particulate air (HEPA) filters in vacuums and air purifiers to capture airborne allergens, which has been shown to decrease respiratory symptoms in atopic individuals by reducing indoor particle levels.^[111]^[112] For food-related atopy, supervised dietary elimination diets may be recommended under medical guidance to identify and avoid specific allergens, though broad eliminations are discouraged due to nutritional risks. Preventive measures, such as consistent barrier protection, can complement these avoidance tactics to enhance overall efficacy.^[110] Pharmacotherapy addresses acute and chronic symptoms through targeted agents suited to the atopic condition. In atopic dermatitis, topical corticosteroids remain the mainstay for inflammation control, often combined with emollients to restore skin barrier function and reduce flare frequency. For asthma, short-acting inhaled beta-agonists provide rapid bronchodilation during exacerbations, while inhaled corticosteroids offer long-term anti-inflammatory effects to prevent progression.^[113] Antihistamines, particularly second-generation H1-blockers, are first-line for allergic rhinitis to alleviate sneezing, itching, and rhinorrhea by blocking histamine-mediated responses.^[35] Biologic therapies represent advanced options for moderate-to-severe cases unresponsive to conventional treatments, targeting key immune pathways. Dupilumab, a monoclonal antibody inhibiting interleukin-4 and interleukin-13 signaling, is approved for atopic dermatitis and severe asthma, achieving significant symptom reduction and skin clearance in clinical trials.^[114] Omalizumab, an anti-IgE antibody, is particularly effective for allergic asthma with high IgE levels, reducing exacerbation rates and corticosteroid dependence.^[114] These agents are administered via subcutaneous injection and are reserved for patients with documented atopy and inadequate response to standard pharmacotherapy.^[115] Allergen-specific immunotherapy (AIT) offers disease-modifying potential through gradual desensitization to allergens. Subcutaneous immunotherapy (SCIT) involves escalating doses of allergen extracts injected over 3-5 years, while sublingual immunotherapy (SLIT) uses daily oral tablets or drops for convenience. Both forms have demonstrated long-term efficacy, with studies reporting 20-30% sustained symptom reduction and decreased medication use in respiratory atopy.^[116]^[117] As of 2025, emerging therapies expand options for refractory atopic dermatitis, including Janus kinase (JAK) inhibitors like abrocitinib, an oral agent that blocks JAK1 to interrupt cytokine signaling and achieve rapid itch relief and skin improvement in moderate-to-severe cases.^[118] Microbiome-based approaches, such as topical probiotics or fecal microbiota transplantation, aim to restore dysbiotic skin or gut communities, showing preliminary promise in reducing inflammation and Staphylococcus aureus overgrowth in early trials.^[119] These innovations underscore ongoing shifts toward personalized, pathway-specific interventions.^[120]

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Allergic rhinitis (AR) is an atopic disease characterized by symptoms of nasal congestion, clear rhinorrhea, sneezing, postnasal drip, and nasal pruritis.
[20]
Atopic Dermatitis: Disease Features, Therapeutic Options, and a ...
Jun 20, 2023 · Aside from eczema, the main symptom of AD is severe itching, which greatly affects patients' daily activities, productivity, and sleep, reducing ...
[21]
Atopic Dermatitis: Diagnosis and Treatment - AAFP
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Atopic Dermatitis - The New England Journal of Medicine
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[23]
Phenotype of Atopic Dermatitis Subjects with a History of Eczema ...
The DACI laboratory performed the following tests on serum samples from all ADEH+ and ADEH- subjects: total IgE (kU/L) and allergen-specific Phadia ImmunoCAP® ...
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Clinical Evaluation of Techniques for Measuring Nasal-Specific ...
Oct 20, 2017 · Serum-specific IgE concentrations ≥ 0.35 kIU/L were considered positive. Peripheral blood total eosinophil counts were checked using an ...Missing: laboratory RAST
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Allergy Testing - StatPearls - NCBI Bookshelf
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Skin prick/puncture testing in North America: a call for standards and ...
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Overview of component resolved diagnostics - PubMed
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Precision medicine in the allergy clinic: the application of ... - PubMed
Feb 12, 2022 · Component-resolved diagnosis (CRD) has solved most of the limitations of extract-based diagnostic procedures and is currently valuable tool for the precision ...
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Filaggrin gene mutations with special reference to atopic dermatitis
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[30]
The persistence of atopic dermatitis and Filaggrin mutations in a US ...
Filaggrin loss-of-function mutations (FLG null) have been associated with an increased risk of developing AD.
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Novel diagnostic approaches and biological therapeutics for intrinsic ...
Jul 8, 2014 · Reviews the diagnostic approach to so-called intrinsic asthma, and evaluates the role of new biological therapies according to the atopy status of asthma.Missing: differential | Show results with:differential
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Type I Hypersensitivity Reaction - StatPearls - NCBI Bookshelf - NIH
Aug 3, 2025 · Type I or immediate hypersensitivity is an exaggerated immunoglobulin E (IgE)-mediated immune response to allergens such as pollen, dust ...
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IgE and mast cells in allergic disease - PMC - PubMed Central
In this review, we discuss findings supporting the conclusion that IgE and mast cells can have both interdependent and independent roles in the complex immune ...
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Type I Hypersensitivity Reaction - PubMed
Aug 3, 2025 · Upon reexposure, the allergen cross-links bound IgE, triggering degranulation and the release of inflammatory mediators. Clinical symptoms vary ...
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This review summarizes the literature surrounding the function and expression of IL-4 and IL-13 in CD4+ T cells and innate immune cells.
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Interleukin-4 and Atopic Dermatitis: Why Does it Matter? A Narrative ...
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The present review aims to highlight recent advances in type 2 immunity and discuss the cellular sources, targets, and roles of type 2 mechanisms in asthma and ...
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The Role of Regulatory T cells in Atopic Dermatitis - PMC - NIH
Regulatory T cells (Tregs) play a pivotal role in immune suppression and are integral to the control of allergic responses.
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T-cell Subset Regulation in Atopy - PMC - PubMed Central - NIH
Th2-derived IL-4 and IL-13 exert an important role in class switching in B lymphocytes that results in IgE production. Recent evidence on T-cell subset ...
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DNA methylation of Th2 lineage determination genes at birth is ...
There is now increasing evidence that asthma and atopy originate in part in utero, with disease risk being associated with the altered epigenetic regulation ...
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Here, we review our current understanding of epigenetics associated with atopic dermatitis. We discuss studies identifying distinct DNA methylation changes.
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Genetic and Epigenetic Aspects of Atopic Dermatitis - PMC - NIH
Recent studies point to the key role of epigenetic changes in the development of the disease. Epigenetic modifications are mainly mediated by DNA methylation, ...
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Interleukin-5 and IL-5 receptor in health and diseases - PMC
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Insight into IL-5 as a Potential Target for the Treatment of Allergic ...
IL-5 has significant effects on allergy and asthma due to its role in eosinophile proliferation and differentiation, which have been well documented [2,4]. To ...
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Basophils as Key Regulators of Allergic Inflammation and Th2-type ...
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Current and Emerging Strategies to Inhibit Type 2 Inflammation in ...
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Pathobiology and Regulation of Eosinophils, Mast Cells, and ...
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[49]
Filaggrin and beyond: New insights into the skin barrier in atopic ...
It is characterized by a dysfunctional skin barrier, which facilitates sophisticated interplay between genetic, immune, microbial, and environmental factors.
[50]
Skin barrier dysfunction measured by transepidermal water loss at 2 ...
Recent studies of high-risk atopic individuals showed that a raised TEWL may precede the clinical manifestation of AD in those at high risk of atopy. A defect ...
[51]
Nonlesional skin in atopic dermatitis is seemingly healthy skin - NIH
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[52]
Claudin-1 Mediated Tight Junction Dysfunction as a Contributor to ...
Jun 29, 2022 · Tight junctions of the airway epithelium include occludin, claudins, ZOs, and JAMs, which regulate the permeablity of epithelial barrier.
[53]
Reduced occludin and claudin-7 expression is associated ... - Nature
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[54]
Epidermal barrier dysfunction and cutaneous sensitization in atopic ...
Recent findings have shown that disruption of epithelial barrier systems are involved in the pathogenesis of immune disorders such as inflammatory bowel ...
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Bacterial and Viral Infections in Atopic Dermatitis: a Comprehensive ...
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[56]
Skin Barrier Abnormalities and Immune Dysfunction in Atopic ... - MDPI
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Type 2 immunity in allergic diseases | Cellular & Molecular ... - Nature
Feb 17, 2025 · Type 2 immunity and eosinophilic esophagitis The disease prominently features a Th2 immune response. EoE strongly correlates with allergies, ...
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Genetics in Atopic Dermatitis: Historical Perspective and Future ...
These data demonstrate that the genetic contribution to the development of AD is substantial and this heritability has been estimated at 70–80% (10, 11) – a ...Missing: polygenic | Show results with:polygenic
[59]
Shared Genetic Architecture Between Atopic Dermatitis and ... - MDPI
... factors [3]. The disease displays significant heritability, estimated at 80% through linkage studies [4]; one of the most established genetic risk factors ...
[60]
Atopic dermatitis: a genetic-epidemiologic study in a ... - PubMed
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[61]
Twin Studies of Atopic Dermatitis: Interpretations and Applications in ...
Sep 2, 2015 · Particularly, the concordance rate of AD is consistently higher for monozygotic (MZ) than for dizygotic (DZ) twins [13], indicating that ...
[62]
Association of IL-4 and ADAM33 gene polymorphisms with asthma ...
The most prominent SNPs of IL-4 and ADAM33 are 589C>T and 400A>G, respectively. There are also controversial reports on the association of these SNPs with ...
[63]
Increased expression of ADAM33 and ADAM8 with disease ...
ADAM33, a disintegrin and metalloproteinase 33 gene, has been identified as a risk factor for asthma and bronchial hyperresponsiveness and has been ...
[64]
Causes of epidermal filaggrin reduction and their role in the ...
We surmise that AD only develops in those filaggrin-deficient subjects who are exposed to environmental triggers, such as low humidity, high-pH surfactants, ...
[65]
Homozygous FLG mutations lead to complete loss of filaggrin ...
For example, different types of heat- ing systems (Schafer et al. , 1999) and low-humidity environments are likely to exacerbate the effects of filaggrin ...<|control11|><|separator|>
[66]
Environmental Changes, Microbiota, and Allergic Diseases - PMC
The development of allergic diseases has been attributed to complex interactions between environmental factors and genetic factors.
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Con: House Dust Mites in Atopic Diseases - ATS Journals
In 1964, Voorhorst and colleagues discovered that dust mites are the major source of allergen in house dust (1) and proposed an association between these mites ...
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https://www.researchgate.net/figure/Homozygous-FLG-mutations-lead-to-complete-loss-of-filaggrin-expression-in-skin_fig1_7078592
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Environmental Triggers of Asthma - CDC Archive
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Long-term exposure to PM2.5 has significant adverse effects on ...
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The hygiene hypothesis: current perspectives and future therapies
Strachan proposed that this increased microbial exposure in early life could protect children from developing immune hypersensitivities later in life. Strachan ...
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Interactions Between Atopic Dermatitis and Staphylococcus aureus ...
Staphylococcus aureus commonly colonizes the skin of atopic dermatitis (AD) patients and contributes to the development and exacerbation of AD.
[73]
Environmental risk factors and their role in the management of ...
Environmental risk factors for atopic dermatitis include prenatal exposures, irritants, climate, pollutants, tobacco smoke, water hardness, urban vs. rural ...
[74]
Atopic Sensitization and the International Variation of Asthma ...
Jul 21, 2006 · The prevalence of asthma symptoms has been shown to vary more than 15-fold among countries worldwide. The international variation in the ...METHODS · RESULTS · DISCUSSION
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Sex-Specific and Long-Term Trends of Asthma, Allergic Rhinitis, and ...
Sep 16, 2024 · Conclusions: Throughout all the periods examined, females consistently exhibited a higher prevalence of AR compared to males. Moreover, the risk ...
[76]
The prevalences of allergic diseases in rural and urban areas are ...
The prevalence of asthma was found as 11.5%, allergic rhinitis as 22.1%, and eczema as 10.7%. Asthma (21.9%), allergic rhinitis (44.3%) and eczema (19.8 ...
[77]
Do socioeconomic factors impact atopic dermatitis outcome? A ...
Oct 10, 2023 · Race and socioeconomic status are thought to influence the severity of atopic dermatitis (AD), but findings differ between countries and measures used.
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Jan 20, 2025 · After pooling all included studies, we noted that the overall prevalence of asthma in children was 10.2% (95% CI: 9.5-11.0%). The prevalence of ...
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Atopic dermatitis - Genetics - MedlinePlus
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The increased prevalence of allergy and the hygiene hypothesis - NIH
Allergic atopic disorders, such as rhinitis, asthma, and atopic dermatitis, are the result of a systemic inflammatory reaction triggered by type 2 T helper (Th2) ...
[82]
(PDF) Asthma prevalence in 1973, 1988 and 2003 - ResearchGate
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[83]
Western Lifestyle and Increased Prevalence of Atopic Diseases
The more easily accessible and thus more "modern" and westernized coastal villages showed a significantly higher prevalence of habitants suffering from atopic ...
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https://e-aair.org/DOIx.php?id=10.4168/aair.2015.7.2.101
[85]
National prevalence of atopic dermatitis in Korean adolescents from ...
May 29, 2024 · However, the most significant decline in prevalence occurred after the COVID-19 pandemic began, with a smaller decline observed during the ...
[86]
Impact of COVID-19 pandemic on adults and children with atopic ...
This review thus aims to systematically evaluate the impact of COVID-19 pandemic-driven changes on AD and FA care, focusing on (1) the impact on AD/FA incidence ...
[87]
The many faces of the hygiene hypothesis
One mechanism frequently associated with the hygiene hypothesis is the skewing of the TH1/TH2 balance away from allergy-promoting TH2 cells toward TH1 cells.
[88]
Skin and oral intervention for food allergy prevention based on dual ...
Regarding food allergy causation, the dual allergen exposure hypothesis proposes that oral allergen exposure leads to immune tolerance, whereas allergen ...
[89]
The Role of the Western Diet on Atopic Dermatitis - NIH
Sep 7, 2023 · In recent decades, there has been a global increase in the prevalence of Western-style diets (WDs) in Europe. These diets include processed ...
[90]
Urbanisation and asthma in low-income and middle-income countries
Jul 5, 2019 · Urbanisation has been associated with temporal and geographical differences in asthma prevalence in low-income and middle-income countries (LMICs).Missing: projections | Show results with:projections
[91]
Global, regional, and national burden of asthma and atopic ...
We expect 275 million (224–330) asthma cases and 148 million (140–158) atopic dermatitis cases in 2050, with population growth driving this increase.Missing: urbanization | Show results with:urbanization
[92]
None
### Key Recommendations on Primary Prevention of Allergic Diseases
[93]
Maternal dietary antigen avoidance during pregnancy or lactation, or ...
Prescription of an antigen avoidance diet to a high‐risk woman during pregnancy is unlikely to reduce substantially her child's risk of atopic diseases.
[94]
The effect of probiotics in the prevention of atopic dermatitis in children
Apr 27, 2023 · In this study, the meta-analysis showed that probiotics can effectively prevent the occurrence of atopic dermatitis (AD).
[95]
Randomized Trial of Peanut Consumption in Infants at Risk for ...
Feb 23, 2015 · The LEAP study showed that early oral introduction of peanuts could prevent allergy in high-risk, sensitized infants and in nonsensitized ...
[96]
Association of atopic dermatitis with smoking: A systematic review ...
Tobacco exposure might be a modifiable risk factor for atopic dermatitis (AD). We examine the association between AD and exposure to tobacco smoke.Abstract · Table I · Discussion
[97]
Dust mite avoidance for the primary prevention of atopic dermatitis
Dust mite avoidance strategies alone or in combination with additional allergen avoidance modalities do not decrease the risk of developing atopic dermatitis.
[98]
Cleaner air could prevent thousands of late-life eczema cases
Oct 9, 2025 · The researchers estimate that almost 16% of late-life eczema cases could be prevented by cutting air pollution in the worst-affected areas. Only ...Missing: regulation public
[99]
BCG Vaccination in Early Childhood and Risk of Atopic Disease
Conclusion. BCG vaccination in early childhood is associated with reduced risk of atopic disease, especially in developed countries.
[100]
Is it Possible to Prevent Atopic Dermatitis?
Apr 2, 2023 · Methods of AD prevention examined in research have focused on improving the skin barrier through use of emollients and moisturizers, reducing exposure to ...What Does Prevention Mean In... · What Is Known About The... · Emollients
[101]
Pathogenesis of allergic diseases and implications for therapeutic ...
Mar 24, 2023 · Current guidelines suggest a combined application of allergen avoidance, pharmacotherapy, and/or allergen-specific immunotherapy (AIT)29,30 ( ...
[102]
Environmental Remediation in the Treatment of Allergy and Asthma
If avoidance of second-smoke is impossible, then using a HEPA filter may be a beneficial and sustainable environmental intervention. Endotoxin. Endotoxin is ...Missing: dietary elimination
[103]
The role of environmental allergen control in the management of ...
Classroom HEPA filters were successful in significantly reducing airborne particles and allergens compared to sham (an air filtration system without a ...Missing: dietary | Show results with:dietary
[104]
Pre-asthma: a useful concept for prevention and disease ... - NIH
Allergic asthma. Allergic asthma often begins in childhood as part of a collection of atopic disorders (atopic dermatitis, food allergy, allergic rhinitis) ...
[105]
Use of biologicals in allergic and type-2 inflammatory diseases ...
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[106]
Precision medicine reaching out to the patients in allergology - NIH
Currently, treatment options for IgE-mediated allergic diseases such as allergic rhinitis, atopic dermatitis, allergic asthma, and food allergy typically ...
[107]
EAACI Allergen Immunotherapy User's Guide - PMC - PubMed Central
AIT for AR can be administered either by the subcutaneous (SCIT) or by the sublingual (SLIT) route. Both SCIT and SLIT have been shown effective in allergic ...
[108]
Mapping the Treatment Journey of Children on Subcutaneous ... - NIH
Oct 2, 2025 · Efficacy categories: Good (>70% symptom reduction), Moderate (30–70 ... Symptom Score; SLIT, sublingual immunotherapy. Data Sharing ...
[109]
Real-World Effectiveness and Safety of Upadacitinib and Abrocitinib ...
Apr 24, 2025 · Emerging systemic JAK inhibitors in the treatment of atopic dermatitis: A review of abrocitinib, baricitinib, and upadacitinib. Drugs ...
[110]
Innovative microbial strategies in atopic dermatitis - PMC
Jul 23, 2025 · Emerging systemic jak inhibitors ... Gut microbiota restoration through fecal microbiota transplantation: A new atopic dermatitis therapy.
[111]
Current insights and trends in atopic dermatitis and microbiota ...
Jun 24, 2025 · Emerging trends from 2020 to 2024 focus on adult AD severity, prebiotics, and personalized interventions like fecal microbiota transplantation ( ...