Identity
Glycolic acid is the alpha-hydroxy acid (AHA) everything else in the family is measured against. At roughly 76 Da it is the smallest common AHA — smaller than lactic, far smaller than mandelic — so it diffuses into the skin the fastest and deepest. That is the source of both its reputation and its risk: it is the strongest surface resurfacer of the AHAs, and also the most likely to sting.
It is a distinct molecule. Lactic acid and mandelic acid are not synonyms of glycolic acid — they are separate, larger, gentler AHAs — and its salts (sodium and ammonium glycolate) are different substances again.
Development & history
- Glycolic acid has long dominated the AHA conversation: it is the benchmark peel acid and the one most people mean when they say "an AHA".
- Its defining feature is molecule size. Being the smallest, it penetrates deepest and works fastest — powerful for resurfacing, but the most irritating and the most photosensitising of the family.
- It is used from beginner-level percentages up to professional peels; high-strength glycolic peels belong in a clinic, not the bathroom.
Mechanism (as proposed)
Glycolic acid is a keratolytic exfoliant: it loosens the bonds ("glue") between dead surface cells so they shed, revealing smoother, more evenly pigmented skin beneath. Because it is the smallest AHA, it penetrates deeper than its cousins, which is why it resurfaces more aggressively and why its results on texture, dullness and the look of fine lines are the most pronounced in the family.
The reference literature goes further — associating glycolic acid with fibroblast stimulation (relevant to the skin's own collagen) and, like other AHAs, with effects on pigment enzymes and comedones. Those mechanisms belong to the reference layer and are described here as such. In this cosmetic entry the claim stays at the level of appearance: the look of smoother, brighter, more even skin from exfoliation and renewal — never "builds collagen", "inhibits tyrosinase" or "treats" any condition. And, as with every AHA, glycolic acid increases sun sensitivity — the deepest-penetrating, so the most of all — which makes daily sunscreen non-negotiable, both to prevent burning and to protect the result.