Lactic acid is an AHA, but its comparison to glycolic acid misses something important: it also acts as a humectant. Lactic acid binds water in the stratum corneum through its hygroscopic properties and is actually a natural component of the skin’s Natural Moisturising Factor (NMF). This dual action – chemical exfoliation and simultaneous hydration – makes it a more balanced option than glycolic acid for skin types that want exfoliation without the dryness.
The exfoliating mechanism is identical to other AHAs: weakening desmosomes between corneocytes in the stratum corneum, accelerating desquamation of dead skin cells. The result is smoother texture, reduced dullness, and over time, stimulation of collagen synthesis in the dermis. The molecular weight is slightly higher than glycolic acid, which means somewhat slower penetration – typically experienced as a gentler exfoliant at equivalent concentrations.
Leave-on products at 5-10% (pH 3.5-4.0) are where most of the research sits. At these concentrations, consistent use over 12+ weeks shows measurable improvements in fine lines, skin texture, and hyperpigmentation. Higher concentrations (15-30%) are used in clinical peels for more aggressive resurfacing.
It’s worth flagging the L- vs. D-lactic acid distinction. L-lactic acid is the biologically active form and what most clinical research used. Some cheaper formulations use a racemic mixture – this is worth checking if you’re comparing product efficacy.
For first-time AHA users, lactic acid at 5-8% is a sensible entry point before moving to glycolic. For anyone managing dry or dehydrated skin alongside dullness or uneven texture, the built-in humectant property makes lactic acid a more practical choice than glycolic acid long-term.