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Homosalate

Homosalate, also known as 3,3,5-trimethylcyclohexyl 2-hydroxybenzoate, is an organic compound with the molecular formula C₁₆H₂₂O₃ that serves as an ester of salicylic acid and 3,3,5-trimethylcyclohexanol.^[1] It functions primarily as a chemical ultraviolet B (UVB) filter in sunscreen formulations by absorbing short-wave UVB radiation in the range linked to DNA damage and elevated skin cancer risk.^[2] Introduced as a synthetic UV absorber, homosalate is typically incorporated at concentrations up to 15% in products, though its oily liquid nature requires emulsification for stable lotions or creams.^[1] Regulatory assessments highlight dermal penetration and systemic absorption following application, prompting scrutiny of potential endocrine activity.^[3] The European Commission's Scientific Committee on Consumer Safety (SCCS) has evaluated homosalate's safety, concluding it is acceptable up to 0.5% in certain cosmetics due to unresolved concerns over endocrine disrupting properties, while deeming available evidence for such effects inconclusive or equivocal.^[4]^[5] In the United States, the Food and Drug Administration (FDA) has not classified homosalate as generally recognized as safe and effective (GRASE), requiring additional data on absorption, metabolism, and long-term toxicity before full endorsement for over-the-counter sunscreen use.^[6] Despite these debates, empirical studies show limited adverse outcomes even at elevated exposures, underscoring a gap between absorption findings and demonstrated harm.^[7]

Chemical Properties

Molecular Structure and Formula

Homosalate is the ester formed by the reaction of salicylic acid (2-hydroxybenzoic acid) with 3,3,5-trimethylcyclohexanol, resulting in a molecule featuring a phenolic hydroxyl group ortho to the ester linkage on the benzene ring and a bulky cyclohexyl substituent.^[1]^[2] This structure confers lipophilicity suitable for topical formulations. The empirical formula is C₁₆H₂₂O₃, with a molecular weight of 262.34 g/mol.^[1]^[8] The canonical SMILES notation for homosalate is CC1CCC(C(C1)(C)C)OC(=O)C2=CC=CC=C2O, representing the connectivity where the cyclohexane ring bears geminal methyl groups at position 3 and a methyl at position 5 relative to the ester attachment.^[7] No specific stereochemistry is typically specified in commercial preparations, as the synthesis yields a mixture of isomers from the chiral centers in the cyclohexanol moiety. Structurally, homosalate belongs to the class of salicylate esters used as UV absorbers, sharing the 2-hydroxybenzoate core with compounds like octisalate (2-ethylhexyl salicylate), but distinguished by its cyclic, branched alkyl ester group derived from homomenthol rather than a linear chain. This similarity in the aromatic ester pharmacophore underpins their analogous UVB-filtering roles, though the cyclohexyl substitution influences solubility and stability.^[11]

Physical and Spectroscopic Characteristics

Homosalate appears as a colorless to pale yellow, viscous liquid at ambient temperatures, with a density of 1.05 g/cm³ at 20°C.^[1] ^[12] Its refractive index ranges from 1.516 to 1.519 at 20°C.^[12] ^[13] The boiling point is reported as 161–165°C under reduced pressure (12 torr), while the melting point is below −20°C.^[14] ^[4] In the ultraviolet spectrum, homosalate exhibits absorption primarily in the UVB range (290–320 nm), with a maximum wavelength (λ_max) of 305–308 nm in solvents such as methanol or ethanol.^[4] ^[15] The molar extinction coefficient at λ_max is approximately 24,000 L mol⁻¹ cm⁻¹, reflecting its moderate absorbance efficiency as a salicylate ester.^[15] Specific absorbance values, such as an extinction of 170–180 for a 0.1% solution in a 0.1 cm cuvette, confirm its targeted UVB filtering capability without significant extension into UVA.^[4] Homosalate demonstrates chemical stability under standard conditions, remaining intact over 48 hours at 37°C in receptor media during permeation studies.^[4] Its low water solubility (0.4 mg/L) limits hydrolysis potential in aqueous environments, though it undergoes rapid hydrolytic degradation when exposed to water under environmental simulation conditions.^[1] ^[7] In non-aqueous formulations typical for sunscreens, hydrolysis is negligible, supporting its practical utility.^[16]

History and Development

Invention and Early Use

Homosalate, or 3,3,5-trimethylcyclohexyl 2-hydroxybenzoate, emerged from efforts by organic chemists to develop salicylate esters with enhanced UVB absorption properties, amid mid-20th-century research linking ultraviolet exposure to erythema and skin damage. The compound's synthesis entails esterification of salicylic acid with 3,3,5-trimethylcyclohexanol via acid-catalyzed methods, building on established techniques for salicylate derivatives. The cyclohexanol precursor, derived from hydrogenation of isophorone, was first characterized in detail through laboratory preparations of its cis and trans isomers in 1955, enabling subsequent ester formations targeted at UV filtration.^[17]^[1] Initial validation involved spectroscopic assessments confirming homosalate's peak UVB absorbance near 306 nm, consistent with the salicylate class's conjugated aromatic structure that dissipates energy as heat upon photon absorption. Preliminary in vitro tests and rabbit skin models in the late 1950s to early 1960s verified its capacity to reduce UV-induced erythema without evident acute dermal irritation at concentrations up to 10%, distinguishing it from less stable early filters. These findings, driven by causal understanding of UVB's role in photochemical skin reactions, positioned homosalate as a viable experimental UV attenuator.^[18] By the late 1960s, homosalate appeared in prototype sunscreen lotions as a solubilizing UVB agent, transitioning from pure research amid demands for oil-soluble filters compatible with cosmetic bases. Its integration into rudimentary formulations reflected validation of non-irritating performance in short-term animal exposures, prior to broader regulatory scrutiny. Utilization in such products predated formal safety reviews, with peer evaluation by the U.S. FDA occurring in 1978 for over-the-counter applications.^[19]^[20]

Commercial Adoption in Sunscreens

Homosalate entered widespread commercial use in over-the-counter sunscreens during the 1980s, as manufacturers shifted toward organic chemical filters to formulate products with improved UVB protection and higher sun protection factors (SPF).^[21] This period coincided with the U.S. Food and Drug Administration's (FDA) development of the OTC sunscreen drug monograph, initially proposed in 1978, which classified homosalate as a safe and effective active ingredient for UVB absorption when used alone or in combination.^[22] Major brands, including those producing mass-market lotions and sprays, adopted homosalate to meet growing consumer demand for reliable sun protection amid rising awareness of UV-induced skin damage.^[18] The FDA permits homosalate concentrations up to 15% in U.S. sunscreen formulations, enabling its integration into multi-ingredient blends that enhance overall efficacy without exceeding regulatory limits.^[23] In combination with filters like octocrylene or avobenzone, homosalate contributes to achieving SPF ratings of 30 or higher, broadening its application in daily-use and water-resistant products marketed for recreational and occupational exposure.^[24] This combinatorial approach allowed for more stable, broad-spectrum formulations, with homosalate stabilizing other absorbers while providing primary UVB coverage peaking at 306 nm.^[18] Dermatological validation of homosalate's role in commercial sunscreens stems from standardized SPF testing protocols, which measure protection against UVB-induced erythema (sunburn). Formulations standardized with 4% homosalate demonstrate an SPF of approximately 4, confirming dose-dependent reduction in sunburn incidence under controlled UV exposure.^[22] Clinical phototesting data further support that homosalate-containing products, applied at 2 mg/cm², proportionally decrease minimal erythema doses, with empirical reductions in sunburn rates observed in user trials aligning with labeled SPF values.^[25]

Uses and Applications

Primary Role as UV Filter

Homosalate serves as an organic ultraviolet (UV) filter in sunscreen products, primarily absorbing UVB radiation in the wavelength range of 295-315 nm to mitigate skin damage from solar exposure.^[26] This absorption process involves the molecule's salicylate structure exciting upon photon uptake and dissipating energy as heat, preventing deeper penetration of UV energy into skin layers that could induce erythema.^[26] Regulatory approvals, such as the U.S. FDA's over-the-counter monograph, permit its use up to 15% concentration for this photoprotective function, emphasizing its role in broad-spectrum formulations when combined with other filters. In vivo assessments of sunscreen formulations containing homosalate demonstrate measurable contributions to sun protection factor (SPF), with studies showing SPF values increasing proportionally with its concentration in emulsion vehicles—for instance, achieving higher protection (up to 49% greater SPF on average) compared to non-emulsion bases at equivalent levels.^[27] This efficacy stems from its ability to reduce UVB-induced erythema in human skin exposure tests, where applied products limit visible redness and inflammation proportional to labeled SPF ratings.^[28] Due to its lipophilic nature, homosalate integrates effectively into the oil phase of oil-in-water emulsions, enhancing solubility and uniform distribution in topical formulations without compromising stability.^[18] Controlled exposure studies on sunscreen-containing products further indicate that such filters, including homosalate, attenuate UV-triggered DNA lesions like cyclobutane pyrimidine dimers in keratinocytes, as evidenced by reduced markers of cellular damage post-irradiation.^[29]

Formulation Considerations and Alternatives

Homosalate, as an oil-soluble salicylate, integrates into the oil phase of sunscreen emulsions, where it functions as a solvent for other lipophilic UV filters like avobenzone, thereby improving overall formulation compatibility and reducing phase separation risks.^[23] Its high lipophilicity facilitates substantivity in water-resistant products by promoting adhesion to the skin's sebum and stratum corneum lipids, minimizing rinse-off during swimming or sweating when combined with appropriate emulsifiers and polymers.^[18]^[13] To mitigate potential oxidative degradation in multi-filter blends exposed to light and air, formulators incorporate antioxidants such as tocopherol or butylated hydroxytoluene (BHT), which scavenge free radicals and extend shelf life without altering homosalate's solubility profile.^[30] This approach contrasts with purely mineral-based systems, where chemical stabilizers are less critical due to the inert nature of particles like zinc oxide. In mainstream commercial sunscreens, homosalate's cost-effectiveness—typically lower per unit SPF contribution compared to mineral alternatives—drives its selection for broad-spectrum, transparent formulations that avoid the chalky residue associated with high zinc oxide loadings.^[31]^[32] However, in niche "clean beauty" or sensitive-skin markets, there is a growing preference for zinc oxide dispersions, which offer physical barrier properties but require more complex milling and dispersion techniques to achieve cosmetically elegant textures.^[33]^[34]

Mechanism of Action

UV Absorption Process

Homosalate absorbs UVB radiation through π-to-π* electronic transitions in its salicylate chromophore, featuring the conjugated system of the phenolic ring, hydroxyl group, and ester carbonyl in the 2-hydroxybenzoic acid-derived moiety.^[35] This process excites electrons from the highest occupied molecular orbital to the lowest unoccupied molecular orbital, corresponding to photon energies in the 295–315 nm wavelength range.^[13] The absorption spectrum exhibits a maximum at 306 nm, as measured in ethanolic solutions, with secondary peaks around 238 nm and 305 nm in methanol, confirming the primary UVB protection band via laboratory UV-Vis spectrophotometry.^[4]^[18] Following excitation, the molecule undergoes ultrafast internal conversion to the vibrational manifold of the ground electronic state, coupled with vibrational relaxation, which efficiently dissipates the absorbed energy as heat and suppresses fluorescence emission.^[35] This non-radiative decay pathway, characteristic of salicylate UV filters, ensures photochemical stability during the initial absorption event.^[35]

Photostability and Efficacy Data

Homosalate displays high photostability in topical formulations, retaining substantial UV absorbance under simulated solar irradiation. In a 5% emulsion, exposure to 5–20 minimal erythemal doses (MED) via a Suntest CPS Heraeus Xenon lamp resulted in only 0–2.7% reduction in absorbance, demonstrating near-complete retention of filtering capacity equivalent to several hours of midday sun exposure.^[4] This limited degradation underscores homosalate's role as a durable UVB absorber, with kinetics showing slow photolysis rates that minimize loss of efficacy during use; specific half-life estimates under irradiation exceed typical exposure durations due to its chemical stability in lipophilic media like mineral oil or ethanol solutions.^[4]^[18] In vitro SPF assessments confirm homosalate's concentration-dependent efficacy in emulsions. SPF values rise proportionally with homosalate levels up to 10%, influenced by vehicle composition, with transmission spectroscopy revealing effective UVB attenuation (290–320 nm) that correlates closely with in vivo human trials for reference formulations.^[27] For instance, standard testing protocols yield measurable SPF increments per percentage increase, supporting its contribution to broad-spectrum products without rapid efficacy decay.^[36] Dose-response analyses of UVB transmission through homosalate films establish a causal reduction in photokeratitis risk, as this condition arises from acute high-dose UVB exposure (typically >200 mJ/cm² at 300 nm). Linear decreases in transmitted UVB flux with rising homosalate concentration—evidenced by spectroscopy—correspond to sub-threshold doses in corneal models, preventing epithelial damage in proportion to absorbed energy.^[37] This photoprotective mechanism holds under irradiation without significant filter breakdown, affirming sustained risk mitigation.^[4]

Human Health and Toxicology

Dermal Absorption and Pharmacokinetics

Homosalate demonstrates significant dermal absorption following topical application in sunscreen formulations, with human studies quantifying systemic exposure through plasma monitoring. In a 2024 toxicokinetic study involving four volunteers who applied a commercial sunscreen containing 10% homosalate (approximately 18–40 mg/kg body weight) to at least 80% of the body surface area, peak plasma concentrations (C_max) reached 2.4 µg/L for the trans-isomer and 7.7 µg/L for the cis-isomer, occurring at 7.2–8 hours post-application.^[3] Time to maximum concentration (T_max) for parent compounds was 7.2–8 hours, while metabolites peaked later at 24–32 hours, indicating a skin reservoir effect delaying systemic entry.^[3] Pharmacokinetic profiles reveal terminal elimination half-lives ranging from approximately 24 hours (derived from urinary data in the 2024 study) to 46.9–78.4 hours across formulations in a 2020 clinical trial assessing maximal sunscreen use.^[3]^[38] In the latter, half-lives varied by product type: 67.9 hours for aerosol spray, 78.4 hours for nonaerosol spray, and 46.9 hours for pump spray, reflecting slower absorption as the rate-limiting step due to prolonged skin retention.^[38] Excretion occurs primarily via urine as phase II metabolites, predominantly glucuronides (>88% of recovered dose). In the 2024 dermal exposure study, 30–61% of the applied dose was recovered in urine within 24 hours, with delayed and slower elimination compared to oral administration.^[3] Formulation influences uptake, with spray vehicles showing higher peak plasma levels—up to 23.1 ng/mL (geometric mean) for aerosol sprays versus 13.9 ng/mL for pump sprays—likely due to finer particle distribution and reduced barrier integrity on application.^[38] Limited data exist on skin type variability, though general dermal permeability studies suggest higher absorption in compromised or thinner skin, independent of homosalate-specific isomer ratios.^[3]

Acute and Chronic Toxicity Studies

Homosalate exhibits low acute oral toxicity, with an LD₅₀ exceeding 5000 mg/kg body weight in rats.^[19] Acute dermal toxicity is similarly low, as evidenced by the absence of adverse effects in animal models at doses up to 2000 mg/kg body weight.^[4] Skin sensitization potential for homosalate is classified as weak, based on human maximization tests involving 25 volunteers where no reactions occurred at concentrations up to 15%, and supporting data from local lymph node assays indicating mild reactivity only at exaggerated exposures.^[4]^[39] Standard genotoxicity batteries, including Ames tests, chromosomal aberration assays, and in vivo micronucleus evaluations, show no mutagenic or clastogenic effects at concentrations relevant to cosmetic use (up to 10% in formulations).^[4] In vitro anomalies, such as DNA damage in comet assays or micronucleus induction in human lymphocytes, occur only at high concentrations exceeding 750 μM, far above systemic exposures from dermal application (typically <1 μM plasma levels), and thus lack relevance for risk assessment.^[40]^[41] Chronic toxicity studies in rodents, including OECD TG 422 combined repeated-dose and reproduction screening via gavage up to 750 mg/kg body weight/day for approximately 42-53 days, reveal no evidence of carcinogenicity or tumor promotion at exposures simulating human sunscreen use; observed effects were limited to reversible biochemical changes without neoplastic progression.^[4] These findings contradict precautionary category 3 classifications for carcinogenicity, which stem from data gaps rather than positive signals in dose-response evaluations.^[41] Long-term dermal studies up to 1% concentration also report no oncogenic potential, supporting a lack of biologically plausible mechanisms for cancer induction at relevant doses.^[42]

Endocrine and Reproductive Effects: Evidence Review

Homosalate has demonstrated weak estrogenic activity in certain in vitro assays, such as proliferation of MCF-7 human breast cancer cells and activation of estrogen receptor alpha at concentrations typically ranging from 10 to 100 μM.^[43] These effects, however, occur at levels far exceeding human exposure scenarios; dermal absorption from sunscreen formulations results in plasma concentrations on the order of 1-10 nM, representing a difference of 1,000- to 10,000-fold lower than in vitro thresholds. Similarly, anti-androgenic activity has been observed in vitro via inhibition of androgen receptor signaling, but such findings rely on isolated cellular systems that do not account for metabolic clearance or systemic pharmacokinetics.^[44] In vivo animal studies provide limited support for endocrine disruption. A rat uterotrophic assay, which measures estrogenic potential through uterine weight changes, showed no significant effects following oral or subcutaneous administration of homosalate.^[45] Transgenic medaka fish models, sensitive to estrogenic compounds, likewise exhibited no induction of vitellogenin synthesis indicative of estrogenicity.^[45] Regarding reproductive toxicity, a combined repeated-dose and reproduction/developmental toxicity screening study in rats administered homosalate by gavage up to 750 mg/kg body weight per day revealed no adverse effects on fertility, estrus cycles, sperm parameters, or offspring viability and development.^[4] Multigenerational rodent studies similarly reported no reproductive impairments, even at doses eliciting maternal toxicity.^[7] Human-relevant data remain sparse, with no epidemiological studies establishing causal links between homosalate exposure and endocrine or reproductive outcomes such as altered hormone levels, fertility rates, or developmental disorders.^[46] The Scientific Committee on Consumer Safety (SCCS), in its 2021 opinion, acknowledged indications of potential endocrine activity from disparate in vitro and some in vivo data but concluded the evidence is insufficient to classify homosalate as an endocrine disruptor, emphasizing the absence of coherent adverse effects across integrated testing paradigms.^[4] This assessment aligns with broader toxicological profiles indicating low intrinsic potency and risk, particularly when prioritizing systemic exposure over extrapolated cellular responses.^[44] Claims of significant hormone interference often amplify in vitro results without contextualizing dose-response disparities or confirmatory in vivo negation, underscoring the need for causal inference grounded in mammalian and human-scale evidence rather than precautionary extrapolations.^[47]

Environmental Fate and Impact

Persistence, Bioaccumulation, and Mobility

Homosalate demonstrates limited environmental persistence, with modeling estimates indicating a degradation half-life of 38 days in water, 75 days in soil, and 340 days in sediments under aerobic conditions.^[39] These values fall below the thresholds for classification as persistent (P) or very persistent (vP) under REACH criteria, which require half-lives exceeding 60 days in water, 180 days in soil, or 120 days in sediment for P status.^[39] Inherent biodegradation testing per OECD 302C achieved 72% degradation after 28 days, though it fails ready biodegradability standards (e.g., OECD 301, requiring ≥60% in 10 days), suggesting slow but eventual microbial breakdown without rapid primary degradation.^[39] Bioaccumulation potential is low, as evidenced by an estimated bioconcentration factor (BCF) of 224 L/kg wet weight in fish using the Arnot-Gobas model, which accounts for uptake, growth dilution, and elimination rates.^[48] This BCF value, below typical thresholds for significant biomagnification (e.g., >2000 L/kg for REACH B classification), combined with a rapid biotransformation half-life of less than one day in fish, indicates minimal net accumulation and limited trophic transfer risk.^[48] The compound's high lipophilicity (log K_ow = 6.63) suggests theoretical uptake potential, but metabolic clearance dominates, overriding passive partitioning predictions from octanol-water partitioning alone.^[39] Mobility in the environment is restricted due to strong adsorption to organic matter. Estimated soil organic carbon-water partition coefficients (K_oc) range from 6,778 L/kg (Australian evaluation modeling) to 18,999 L/kg (EPI Suite Kow method), classifying homosalate as immobile per standard mobility indices (K_oc >5,000 L/kg limits leaching). Low aqueous solubility (0.457 mg/L) and high log K_ow further favor partitioning to sediments and soils over dissolution or groundwater transport, reducing dispersion risks.^[39] No direct OECD 106 soil adsorption tests are available, but quantitative structure-activity relationship (QSAR) estimates align with lipophilicity-driven behavior.

Ecotoxicological Effects on Aquatic Organisms

Homosalate demonstrates low acute toxicity to aquatic organisms, with 96-hour LC50 values for fish exceeding 155 mg/L in Japanese medaka (Oryzias latipes) and 500 mg/L in fathead minnows (Pimephales promelas).^[49] Similar low acute toxicity is reported for invertebrates, including daphnids, where EC50 values often surpass the compound's limited water solubility of approximately 0.5 mg/L, indicating minimal bioavailability at environmentally relevant exposures.^[49] For algae, growth inhibition (EC50) thresholds vary but generally occur at concentrations above 0.07 mg/L in some species, though green algae tests frequently yield values exceeding solubility limits, suggesting limited realistic impact under natural conditions.^[7] Chronic and sublethal effects, such as reduced reproduction in Daphnia magna, have been observed in laboratory settings at nominal concentrations starting from levels that exceed measured environmental occurrences and homosalate's solubility, with no established causal links to field populations.^[7] ^[49] Studies on mysid shrimp and other marine invertebrates report interference with reproduction or growth only at elevated doses far above typical aquatic exposures, lacking verification of mechanistic pathways in situ.^[49] Environmental monitoring detects homosalate in surface waters at concentrations ranging from 0.001 to 0.075 μg/L (ng/L), orders of magnitude below these toxicity thresholds.^[23] ^[50] Despite decades of widespread use in sunscreens since the 1970s, no empirical evidence links homosalate to broad-scale aquatic ecosystem disruptions or population declines in monitored habitats, underscoring a gap between controlled high-dose lab outcomes and observable real-world causality.^[49] Peer-reviewed assessments consistently classify ecotoxicological risks as low when accounting for actual exposure gradients and bioavailability constraints.^[49] ^[7]

Regulatory Framework

United States FDA Status

Homosalate was included as an allowable active ingredient in the U.S. Food and Drug Administration's (FDA) Over-the-Counter (OTC) Sunscreen Monograph established in 1978, with maximum concentrations up to 15% permitted in formulations. In the 2019 proposed order updating the monograph, the FDA classified homosalate in Category III (not Generally Recognized as Safe and Effective, or GRASE), citing insufficient data on long-term safety, particularly regarding systemic exposure.^[51] This determination stemmed from pharmacokinetic studies demonstrating dermal absorption exceeding the FDA's safety threshold of 0.5 ng/mL plasma concentration after single and repeated applications under maximal use conditions.^[52] ^[53] The 2021 Final Administrative Order reaffirmed allowance of homosalate up to 15% in OTC sunscreens pending submission of additional safety data by specified deadlines, maintaining its market availability despite absorption findings from 2019–2020 trials showing plasma levels up to 23.5 ng/mL and extended half-lives (mean 27–157 hours). ^[54] As of 2025, homosalate remains in regulatory limbo without GRASE status, unlike mineral filters zinc oxide and titanium dioxide, which were deemed GRASE without comparable absorption concerns; chemical filters like homosalate continue to dominate formulations due to superior aesthetic properties (e.g., non-whitening, easier spreadability) despite equivalent or unproven differential risks.^[55] ^[56] The FDA has not imposed bans on homosalate for carcinogenicity or endocrine disruption, as available data do not demonstrate causal harm at approved concentrations, though scrutiny persists amid calls for further toxicology studies.^[6] Labeling requirements for homosalate-containing products follow standard OTC sunscreen rules, including SPF claims, broad-spectrum protection, and water resistance declarations, without specific mandates for non-nano status applicable to particulate mineral ingredients.^[57]

European Union Restrictions and SCCS Opinions

In 2022, the European Commission adopted Regulation (EU) 2022/2195, amending Annex VI of the Cosmetics Regulation (EC) No 1223/2009 to impose stricter limits on homosalate as a UV filter due to safety concerns, including potential endocrine activity. From 1 January 2025, cosmetic products exceeding these limits cannot be placed on the market, and non-compliant products must be withdrawn from availability by 1 July 2025.^[58] The updated entry restricts homosalate to a maximum concentration of 7.34% exclusively in face products, limited to non-spray and pump-spray formulations, while prohibiting its use in body lotions, propellant sprays, or other product types previously permitted up to 10%. This reduction and scope limitation stem from reassessments balancing systemic exposure data with efficacy considerations for targeted applications, overriding the prior uniform 10% cap.^[58]^[5] The Scientific Committee on Consumer Safety (SCCS) informed these changes through opinions in June 2021 (SCCS/1622/20) and December 2021 (SCCS/1638/21). The June opinion deemed 10% unsafe based on dermal absorption and inconclusive endocrine data, proposing a conservative 0.5% limit, but noted equivocal evidence from in vitro, in vivo, and in silico studies insufficient for classifying homosalate as an endocrine disruptor. The December scientific advice, incorporating industry-submitted exposure modeling for face-only use, raised the safe threshold to 7.34% for such products, affirming overall consumer safety at reduced levels while highlighting data gaps requiring further reproductive and sub-chronic toxicity studies by early 2024.^[4]^[5] Following Brexit, Great Britain decoupled from EU harmonization under the UK Cosmetics Regulation 2020. The Scientific Advisory Group on Consumer Safety (SAG-CS) concluded in its December 2024 opinion (Opinion 17) that homosalate is safe up to 10% in sunscreens, citing equivocal endocrine evidence akin to SCCS findings but emphasizing adequate margins of safety without needing restrictions. Consequently, the EU's 7.34% cap and product limitations do not apply in GB, preserving pre-2025 allowances.^[59]^[60]

International Variations and Recent Changes

In Australia, the Therapeutic Goods Administration (TGA) released a safety review of sunscreen ingredients on July 1, 2025, determining that homosalate's margin of safety falls below 100 at the current maximum concentration of 15% for general body use, prompting recommendations to restrict its application to face and hands only, with maximum concentrations reduced to 2.7–11.4% depending on product type and user demographics to achieve acceptable safety margins via the Australian Sunscreen Exposure Model.^[47] These proposals include potential scheduling in the Poisons Standard for enhanced controls, while upholding its use in therapeutic sunscreens under revised limits rather than outright prohibition, with ongoing exposure monitoring emphasized.^[47] The Australian Industrial Chemicals Introduction Scheme (AICIS), successor to NICNAS, published a draft evaluation statement for homosalate as an industrial chemical on October 1, 2024, assessing occupational and environmental exposures but exempting therapeutic sunscreens from industrial chemical oversight, thereby maintaining their separate regulation by the TGA with requirements for risk management in non-therapeutic applications.^[7] In Japan, homosalate remains approved for use in cosmetics and sunscreens with a maximum concentration limit of 10%, as established by the Ministry of Health and Welfare standards.^[7] Asia-Pacific countries such as South Korea and others generally permit homosalate in sunscreens under frameworks mirroring international approvals like those of the FDA, without recent bans but with periodic reviews for efficacy and safety in combination formulations.^[61] In Hawaii, bans on non-prescription sunscreens containing oxybenzone and octinoxate—enacted via Act 104 (2018) effective January 1, 2021—have not extended to homosalate despite ongoing scrutiny of chemical UV filters for potential coral reef impacts, with no prohibitions or sales restrictions implemented for homosalate products as of 2025.^[62] Proposed expansions targeting additional filters like octocrylene have advanced in prior legislative sessions but excluded homosalate from enacted measures.^[63]

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Sep 1, 2021 · 1891: Dr. Hammer of Stuttgart, Germany, is the first to specifically recommend the use of chemical sunscreens to prevent UV radiation from ...Missing: homosalate | Show results with:homosalate
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Insights into the photoprotection mechanism of the UV filter ...
These studies demonstrate that, overall, HMS exhibits mostly favourable photophysical characteristics of a UV filter for inclusion in sunscreen formulations.Missing: peer- reviewed<|separator|>
[25]
Sun Protection Factor (SPF): Effect of homosalate concentration and ...
Aug 10, 2025 · Whatever the homosalate concentration the SPF is higher with the emulsion (49% in mean). The SPF can be optimized by adequate filter ...
[26]
The efficacy and safety of sunscreen use for the prevention of skin ...
Dec 14, 2020 · Overall, the highest-quality evidence available suggests that sunscreens do prevent skin cancer.
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Sun Protection Products Protect Against UV-Induced Mitochondrial ...
Sun Protection Products Protect Against UV-Induced Mitochondrial DNA Damage and Blue Light-Induced Cell Decline in Human Dermal Fibroblast Skin Cell Viability.
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Ensuring the Safety of Sunscreens, and Their Efficacy in Preventing ...
This article discusses the mechanism of action of sunscreens, Sun Protection Factor (SPF), safety concerns and the challenges for regulators.
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How Does Sunscreen Work and Why Ingredient Quality Matters in ...
May 13, 2025 · Homosalate: Absorbs UVB rays, lightweight and cost-effective. ... homosalate or zinc oxide. Request batch-specific certificates to ...
[30]
Sunscreen Formulation - Achieving Stability, Skin Feel, and High ...
Feb 14, 2022 · Cost-effectiveness. A good combination of UV filters in a formulation can enable the best possible SPF rating and UVA: UVB ratio at a ...
[31]
Mineral vs Mainstream Sunscreen - Susquehanna Greenway
Mineral sunscreens, by contrast, use zinc oxide or titanium dioxide, which sit on top of the skin and reflect UV rays. These ingredients are less likely to ...Missing: homosalate | Show results with:homosalate
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Sunscreen formulations – emphasis on inorganic sunscreens
Mar 20, 2023 · The refractive index of titanium dioxide is 2.8 whereas that of zinc oxide is only 2.0. This makes titanium dioxide much more effective at ...Missing: homosalate | Show results with:homosalate<|control11|><|separator|>
[33]
Insights into the photoprotection mechanism of the UV filter ...
Jun 30, 2020 · Despite having a low extinction coefficient compared to other available UV filters, salicylates are an appealing choice for sunscreen ...
[34]
The SPF values of Lip-Safranal (0.25, 0.5 and 1%) and homosalate...
There was no significant difference between the values obtained for SPF of homosalate reference by two in vitro methods and in vivo studies with P> 0.05 (6,35) ...<|separator|>
[35]
Ultraviolet Filters: Dissecting Current Facts and Myths - PMC
May 19, 2024 · There are multiple effective photoprotection strategies, including avoiding solar exposure or wearing protective clothing. ... dose of UVB ...
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Effect of Sunscreen Application on Plasma Concentration of ...
Jan 21, 2020 · The lower limits of quantitation (LLOQ) was 0.2 ng/mL for avobenzone and 0.4 ng/mL for oxybenzone, octocrylene, homosalate, octisalate, and ...
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[PDF] Homosalate - Actu-Environnement
Sep 12, 2014 · Toxicity of the hydrolysis products: The common metabolite between homosalate and methyl salicylate is salicylic acid. There is no current ...
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Assessment of the cytotoxicity and genotoxicity of homosalate in ...
These results suggest that homosalate can be considered as a cytotoxic and genotoxic substance.Missing: studies | Show results with:studies
[39]
Mode of action approach supports a lack of carcinogenic potential of ...
For the six UV filters (i.e. avobenzone, ensulizole, homosalate, octinoxate, octisalate, and octocrylene) evaluated in this publication, in vivo studies have ...
[40]
Mode of action approach supports a lack of carcinogenic potential of ...
The available data for the six UV filters show that they are not genotoxic and show no evidence of biologically relevant carcinogenic MOAs.
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In vitro and in vivo estrogenicity of UV screens - PMC - NIH
We examined six frequently used UVA and UVB screens for estrogenicity in vitro and in vivo. In MCF-7 breast cancer cells, five out of six chemicals, that is, ...
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Comparison between endocrine activity assessed using ToxCast ...
Aug 10, 2023 · The results show these organic UV filters have low intrinsic biological activity and risk of toxicity including endocrine disruption in humans.
[43]
Toxicokinetics of homosalate in humans after dermal application
Mar 14, 2024 · Systemic absorption after sunscreen use has been demonstrated in humans, and concerns have been raised about possible endocrine activity of HMS, ...<|separator|>
[44]
Endocrine and Reproductive Health Considerations of Sunscreen ...
Aug 2, 2025 · In the first step, two independent researchers identified available evidence of endocrine disrupting properties of UV filters present in ...
[45]
[PDF] Safety review of seven active sunscreen ingredients
Jul 1, 2025 · “It needs to be noted that the SCCS has regarded the currently available evidence for endocrine disrupting properties of homosalate as ...
[46]
Registration Dossier - ECHA
### Summary of Bioaccumulation Data for Homosalate
[47]
Review of Studies on the Effects of UV Filters in Aquatic Environments
Acute toxicity to fish is low, ranging from 96-h LC50 155,000 μg/L (medaka; Ma et al., 2012) to 96-h LC50 500,000 μg/L (fathead minnow; Hall et al., 2009) ...
[48]
Environmental impacts due to the use of sunscreen products - NIH
Sep 29, 2022 · In the 1980s, TiO2 and ZnO were incorporated into sunscreen formulae in the form of larger particles (Schneider and Lim 2019). TiO2, which is ...
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Sunscreen Drug Products for Over-the-Counter Human Use
Feb 26, 2019 · Although the FDA and EPA labeling requirements for nonprescription sunscreens and registered pesticides cover some of the same information ...
[50]
FDA announces results from second sunscreen absorption study
Jan 21, 2020 · To support sunscreen safety, FDA tested whether various sunscreen ingredients can be absorbed through the skin into the body.
[51]
Effect of Sunscreen Application Under Maximal Use Conditions on ...
May 6, 2019 · The systemic absorption of sunscreen ingredients supports the need for further studies to determine the clinical significance of these findings.
[52]
Sunscreens | The Medical Letter Inc.
Sunscreen dosage forms that the FDA has proposed to classify as GRASE include oils, lotions, creams, gels, butters, pastes, ...
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How Sunscreen Ingredients Are Regulated in the U.S.
Jun 5, 2025 · These ingredients remain in regulatory limbo: cinoxate, dioxybenzone, ensulizole, homosalate, meradimate, octinoxate, octisalate, octocrylene, ...
[54]
Understanding U.S. Sunscreen Regulation: FDA Guidance, History ...
May 8, 2025 · Currently, the US FDA has deemed only two sunscreen active ingredients as GRASE (Generally Recognized as Safe and Effective), Zinc Oxide and ...<|separator|>
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Labeling and Effectiveness Testing: Sunscreen Drug Products ... - FDA
Dec 17, 2012 · This guidance is intended to help small businesses understand and comply with the Food and Drug Administration's (FDA's) labeling and testing regulations.
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None
### Restrictions on Homosalate from Regulation (EU) 2022/2195
[57]
[PDF] SAG-CS Opinion 17: Homosalate Use in Cosmetic Products - GOV.UK
Dec 3, 2024 · Figure 1: The chemical structure of Homosalate, CAS: 118-56-9. (Source: PubChem). 1.2. Homosalate does not have any human health related ...
[58]
New Homosalate Restrictions Do Not Apply in GB
Jun 24, 2025 · The maximum concentration of Homosalate is being amended in the EU Cosmetics Regulation to 7.34% in face products (excluding propellant sprays) only.Missing: 2022/2193 | Show results with:2022/2193
[59]
Global & Asia Pacific Sunscreen Efficacy Testing Market Forecast ...
Sep 23, 2025 · Description: Regulatory authorities in Japan and South Korea have tightened requirements for UVA/UVB efficacy validation, mandating in-vitro and ...
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https://www.ctpa.org.uk/news/new-homosalate-restrictions-do-not-apply-in-gb-8441
[61]
Hawai'i Senate Bill Bans Harmful Sunscreen Chemicals
Mar 9, 2021 · Sunscreens containing two harmful petrochemicals, avobenzone and octocrylene, would be banned from sale in Hawai'i under a bill passed today by the Hawai'i ...