Lactic Acid

Lactic acid is an alpha hydroxy acid traditionally derived from fermented milk, the same compound responsible for milk's slightly sour taste. Today, cosmetic-grade lactic acid is usually produced through bacterial fermentation of plant sugars rather than directly from dairy. Compared with glycolic acid, its molecule is larger and penetrates the surface less aggressively. This is why it has a reputation as a gentler AHA.

Like other AHAs, lactic acid loosens the bonds between dead surface cells and accelerates their shedding. Its larger molecular size limits penetration depth compared with glycolic acid, resulting in gentler renewal and usually less irritation. It also has a documented humectant effect, which is unusual for an AHA: it hydrates the surface while exfoliating. This combination makes it a common choice for sensitive skin beginning with AHAs.

For sensitive or dry skin and first-time AHA users who want surface renewal with a gentler, more hydrating profile than glycolic acid.

The same sun-sensitivity warning applies as with every AHA. Daily SPF is essential because exfoliated skin is more vulnerable to UV damage regardless of which acid is doing the exfoliating.