Lactic Acid

Evidence by route

Working concentrations

About this ingredient

Lactic Acid is a two-carbon alpha-hydroxy acid (AHA), a natural metabolite of lactic fermentation. Found in sour milk (hence the name), kefir, and in human sweat. Produced synthetically or by Lactobacillus fermentation. Mechanism. At low pH (3.5-4.0) it loosens desmosomal bonds between corneocytes in the stratum corneum – cells shed more easily. This reduces hyperkeratosis, evens out texture, and lightens pigmentation. Additionally lactic acid is a component of the natural moisturizing factor (NMF), binds water, and hydrates the stratum corneum. This dual effect distinguishes it from glycolic acid (which only exfoliates). Where applied. Exfoliants, toners, creams, masks (5-10% in cosmetics, up to 20-30% in peel formulas). Professional dermatological peels – 30-70%. In Spain – Sesderma Acglicolic, The Ordinary Lactic Acid 5%/10%, Mesoestetic Glycolic Solution, Avène Cleanance ACne Mask. Evidence base. Smith 1996, Stiller 1996, Tasic-Kostov 2010 – RCTs with 5-12% lactic acid in photoaged patients: improved texture, reduced fine wrinkles, lightened pigmentation over 12 weeks. Less irritating than glycolic acid at comparable efficacy. Well suited for dry and sensitive skin. Safety. CIR rated lactic acid safe at cosmetic concentrations up to 10% at pH ≥3.5 (1998, re-evaluated 2017). EU SCCS confirmed safety. Irritation possible at high concentrations and low pH – especially in the first weeks of use. Increases photosensitivity – SPF 30+ during the day is mandatory. Pregnancy and lactation – safe topically at cosmetic concentrations. Suitable for dry, sensitive, mature skin, for pigmentation, post-inflammatory hyperpigmentation, ichthyosis. With active rosacea and herpes – use with caution.

Tolerability and safety

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