AHA (glycolic/lactic)

AHAs, or alpha hydroxy acids, are water-soluble exfoliating acids, most commonly glycolic acid (the smallest molecule, so it penetrates most readily) and lactic acid (which also has a humectant, hydrating quality). Glycolic derives originally from sugar cane and lactic from milk fermentation, though cosmetic grades are made to spec. They work by loosening the bonds between dead surface cells, encouraging a smoother, brighter surface. The evidence is strong. AHAs are well studied for improving texture, radiance, fine lines and the look of uneven tone, and glycolic acid in particular has substantial clinical backing for photoaging. Results are reliable when frequency is sensible. They are best for normal to combination skin dealing with dullness, roughness and early aging, with lactic acid a gentler entry for drier or more sensitive skin. They map to texture and dullness concerns. Layering requires some care. Start two to three times a week and build tolerance. Pair AHAs with hydrators and barrier support such as hyaluronic acid, panthenol and ceramides. Avoid using them in the same session as retinoids, and generally do not stack multiple strong exfoliants at once, since that invites irritation and barrier damage; alternate nights instead. Daily broad-spectrum SPF is mandatory because exfoliation increases sun sensitivity. On safety, expect possible tingling; overuse causes stinging, redness and a compromised barrier, so more is not better. They do not feed Malassezia. Topical AHAs are generally considered acceptable during pregnancy, but confirm with your clinician, and always protect exfoliated skin from the sun.