Lactic acid

Lactic acid is a natural component of the skin's own humectant mix. As an exfoliant it works like glycolic acidGlycolic acidModerateGlycolic Acid · Alpha-hydroxy acidSmallest AHA, deepest penetration; solid photoageing data at 8–10 % with pH doing much of the work.Open in the Index → but penetrates more slowly, which is why it tends to sting less.

The evidence

In the same 22-week trial that established 8 % glycolic acid, 8 % lactic acid produced equivalent improvements in photodamage[1]. A separate study of 12 % lactic acid reported increased epidermal and dermal firmness and a rise in stratum corneum ceramides[2], though that result has not been widely replicated.

Pair with ureaUreaStrongUrea · Natural moisturising factorHumectant at 2–10 %, keratolytic at 20–40 %; one of the oldest evidence-based moisturising actives.Open in the Index → for rough, dry skin; alternate with retinolRetinolStrongRetinol · Vitamin A alcoholThe best-evidenced over-the-counter retinoid for photoageing; now capped at 0.3 % in EU leave-on products.Open in the Index →.