Glycolic Acid
Also known as Glycolic acid, Hydroxyacetic acid, 2-Hydroxyacetic acid, Alpha-hydroxyacetic acid, Ethylene glycolic acid
“CIR Expert Panel says: safe within use limit.”
Glycolic Acid (2-hydroxyacetic acid; CAS 79-14-1; C2H4O3) is the smallest alpha-hydroxy acid (AHA) and the most widely studied cosmetic exfoliant. It acts by reducing corneocyte cohesion in the stratum corneum, accelerating desquamation and promoting cell turnover — effects that are strongest in the un-ionized form at low pH (optimal turnover at pH 2.8–4.8). The CIR Expert Panel assessed glycolic acid together with lactic acid, their common salts, and simple esters (IJT 17(S1):1-241, 1998; updated IJT 36(Suppl 2):14-58, 2017) and concluded these ingredients are safe at concentrations up to 10% at pH ≥ 3.5 for consumer leave-on products with sun-sensitivity labelling, and up to 30% at pH ≥ 3.0 for brief-contact salon professional use. The EU SCCNFP issued a more conservative precautionary position (SCCNFP/0370/00, June 2000; reaffirmed SCCNFP/0799/04, May 2004) recommending glycolic acid not exceed 4% at pH ≥ 3.8 in consumer products, based on UV photosensitivity concerns and incomplete long-term safety data. The SCCNFP precautionary limits are substantially more restrictive than the CIR consumer-tier limits, reflecting the precautionary principle rather than an established NOEL. FDA clinical studies (cited in SCCNFP/0370/00) demonstrated that 10% glycolic acid at pH 3.5 applied for 4 weeks significantly increased sunburn cell formation and reduced the minimal erythema dose — photosensitivity effects that reversed within 1 week of stopping treatment. A 2024 skin equivalent model study confirmed high-concentration glycolic acid (35%) causes time-dependent disruption of epidermal structural proteins including filaggrin, involucrin, and loricrin, providing mechanistic insight into chemical peel dynamics. Glycolic acid is not formally listed in EU Annex III as a restricted substance; the 4%/pH 3.8 guidance remains a precautionary scientific committee recommendation rather than a binding regulatory restriction.
AHA exfoliant — the smallest and most water-soluble AHA, with superior skin penetration relative to larger AHAs; accelerates stratum corneum cell turnover by reducing intercorneocyte ionic bonding, effective for photoaged skin, hyperpigmentation, acne, and rough texture.
Collagen stimulation: at exfoliant-active concentrations, promotes collagen synthesis and elastin production in the dermis; used in anti-aging formulations for wrinkle reduction.
Well-characterised safety profile: dual CIR/SCCNFP safety assessments covering the full concentration range from consumer cosmetics (≤10%) through professional peels (up to 30/35%); mechanism of action thoroughly understood.
CIR consumer-tier approval: safe at ≤10%, pH ≥ 3.5, with sun-protection labelling — covers the full range of typical OTC AHA exfoliant formulations.
pH-adjusting function: glycolic acid is widely used as a pH adjuster in cosmetic formulations to bring product pH to the range optimal for other actives (e.g., vitamin C, retinoids, peptides), even when not functioning as a primary exfoliant.
Long history of dermatological use since the 1990s; extensively studied in clinical and laboratory settings with no systemic toxicity at cosmetically relevant exposure levels.
- · Long-term UV safety data were incomplete at the time of the SCCNFP/0370/00 review; no NOEL has been established for the UV photosensitivity effect at consumer-use concentrations.
Increases skin UV sensitivity: FDA clinical studies showed 10% glycolic acid at pH 3.5 applied for 4 weeks caused statistically significant increases in sunburn cell formation (SBC) and reductions in minimal erythema dose (MED); effects reversed within 1 week of cessation. Both CIR and SCCNFP require sun-protection labelling for leave-on AHA products.
SCCNFP precautionary limit (4%, pH ≥ 3.8) is substantially more conservative than CIR consumer-tier limit (10%, pH ≥ 3.5); the inter-jurisdictional conflict reflects different risk frameworks — precautionary principle vs. weight-of-evidence — not a safety determination against either limit.
Skin irritation: highly pH-dependent; stinging, tingling, and scaling reported at concentrations ≥4–8% especially at low pH. Facial discomfort studies at concentrations 2–10% and pH 3.3–6.1 showed response is more strongly correlated with pH than concentration alone.
High-concentration professional peels (35%+) cause time-dependent disruption of epidermal structural proteins (filaggrin, involucrin, loricrin, KLK10, AQP3); not a concern at consumer cosmetic concentrations but relevant to professional use context.
Penetration-enhancement potential: AHAs may increase percutaneous absorption of other cosmetic ingredients (e.g., Benzophenone-3/oxybenzone); no barrier damage observed at 5% glycolic acid pH 3.8, but relevant for formulations combining glycolic acid with other actives.
CIR Quick Reference Table (October 2024) — Glycolic Acid row: Finding=SQ, Citation=IJT 17(S1):1-241, 1998; IJT 36(Suppl 2):14-58, 2017
“Based on the available information included in this report, the CIR Expert Panel concludes that Glycolic and Lactic Acid, their common salts and their simple esters, are safe for use in cosmetic products at concentrations less than or equal to 10%, at final formulation pH greater than or equal to 3.5, when formulated to avoid increasing sun sensitivity or when directions for use include the daily use of sun protection. These ingredients are safe for use in salon products at concentrations less than or equal to 30%, at final formulation pH greater than or equal to 3.0, in products designed for brief, discontinuous use followed by thorough rinsing from the skin, when applied by trained professionals, and when application is accompanied by directions for the daily use of sun protection...Glycolic Acid...”— QRT-Update-100824_0.pdf, Glycolic Acid row (Conclusion column), p. 18
SCCNFP Position Paper on the Safety of Alpha-Hydroxy Acids (SCCNFP/0370/00, final), adopted 28 June 2000, 13th plenary meeting
“glycolic acid may be used safely at a level of up to 4% and a pH >= 3.8 lactic acid up to a maximum level of 2.5% and a pH >= 5 Further, it is recommended that their should be appropriate warnings to the consumer of : * avoiding contact with the eyes * avoiding / or affording protecting from UV whilst using products containing AHAs because of the suggestion of susceptibility to increased damage from UV whilst cosmetic products containing them are being used.”— SCCNFP/0370/00 final, p. 8 (Discussion section)