Lactic Acid
Also known as L-Lactic acid, 2-Hydroxypropanoic acid, Alpha-hydroxypropionic acid, Milk acid
“CIR Expert Panel says: safe within use limit.”
Lactic Acid (2-hydroxypropanoic acid; CAS 50-21-5; C3H6O3) is an alpha-hydroxy acid (AHA) naturally present in the skin's Natural Moisturising Factor (NMF) and produced commercially by fermentation of carbohydrates. In cosmetic formulations at exfoliant-active concentrations (typically 2–10%), it functions as a keratolytic by reducing intercorneocyte cohesion and accelerating stratum corneum cell turnover; at lower concentrations or in its salt form (sodium lactate), it acts as a humectant. The CIR Expert Panel assessed lactic acid together with glycolic acid, their common salts, and simple esters (AHA group assessment, originally 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 leave-on consumer products, with sun-sensitivity labelling required, 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 lactic acid not exceed 2.5% at pH >= 5.0 in consumer products, based on concerns about AHA-induced UV photosensitivity and incomplete long-term safety data. The SCCNFP limits are substantially more restrictive than the CIR consumer-tier limits, reflecting the precautionary principle rather than a dose-response NOEL. The FDA has confirmed sun-sensitivity concerns for AHA-containing products and requires labelling guidance. Both the CIR 10%/pH 3.5 consumer limit and the SCCS 2.5%/pH 5.0 limit are current and unresolved.
AHA exfoliant — accelerates stratum corneum cell turnover by reducing intercorneocyte ionic bonding; effective for photoaged skin, hyperpigmentation, and rough texture at clinical concentrations
Humectant and NMF component at lower concentrations: sodium lactate (lactic acid salt) is a primary NMF constituent and is well-tolerated in moisturising formulations
Well-characterised safety profile across both the CIR AHA group assessment:14-58, 2017) and SCCS/SCCNFP position papers (0370/00 and 0799/04)
CIR consumer-tier approval: safe at <=10%, pH >= 3.5, with sun-protection labelling — covers the full range of typical OTC AHA exfoliant formulations
Long history of dermatological use; naturally occurring metabolite (Krebs cycle, NMF) with no systemic toxicity at cosmetically relevant exposure levels
Increases skin UV sensitivity (increased sunburn cell formation and reduced minimal erythema dose demonstrated at >=4% glycolic acid, pH 3.5 — used as AHA class proxy for lactic acid): both CIR and SCCS require sun-protection labelling for leave-on AHA products
SCCS precautionary limit (2.5%, pH >= 5.0) 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
Stinging, tingling, and irritation reported at concentrations >8% and low pH, especially in sensitive skin; 26% of subjects perceived irritation at 0.5% lactic acid/glycolic acid mixture applied to face daily for 6 weeks (per SCCNFP/0370/00 citation)
The SCCNFP notes that no NOEL (no-observed-effect level) was identified for UV sensitivity effects in the studies reviewed; precautionary limits therefore represent conservative upper bounds, not established safety thresholds
CIR Quick Reference Table (October 2024) — Cetyl Lactate row encoding AHA group assessment conclusion for Glycolic and Lactic Acid: Findi…
“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...Cetyl Lactate...”— QRT-Update-100824_0.pdf, Cetyl Lactate row (Conclusion column)
SCCNFP Updated Position Paper Concerning Consumer Safety of Alpha-Hydroxy Acids (SCCNFP/0799/04), adopted 25 May 2004, 28th plenary meeting
“The SCCNFP maintains its previous opinion (SCCNFP/0370/00, 28 June 2000) because of the inadequate nature of the data submitted for evaluation. [From SCCNFP/0370/00:] lactic acid up to a maximum level of 2.5 % and a pH >= 5”— SCCNFP/0799/04, Section 5 (Conclusion); SCCNFP/0370/00, Section 2 (Position of the SCCNFP, Discussion paragraph)