Glycolic acid

What does glycolic acid do for skin?

Glycolic acid is for skin that feels rough and looks tired: a sandpapery forehead, a dull cast that makeup sits on badly, or forearms that look thin and creased after years of sun. It speeds up the shedding of the worn top layer, so the surface looks smoother and brighter.

The longest look at what happens underneath is a 6-month forearm study. People put a lotion with 25% glycolic, lactic or citric acid on one forearm and a placebo on the other. The treated skin became about 25% thicker, with denser collagen and better-quality stretchy fibers, and without signs of inflammation.

How does glycolic acid work?

The visible part is simple: dead cells on the surface let go sooner, so rough patches and dullness wear away. What happens deeper is less settled. A review of hydroxy acids notes that, despite decades of use, “their biological mechanism(s) of action still require more clarification.” Glycolic acid belongs to a family that also includes lactic acid, salicylic acid and gentler polyhydroxy acids. A 2012 review describes AHAs, glycolic acid in particular, as proven ingredients for uses ranging from hydration to breakouts, with results depending on the concentration.

Does glycolic acid make you more sensitive to the sun?

Yes. In a double-blind study, 29 people applied 10% glycolic acid at pH 3.5, or a placebo, to their backs 6 days a week for 4 weeks. The glycolic sites burned more easily: more sunburned cells formed and less UV was needed to turn skin red. The extra sensitivity was gone within a week of stopping. In practice, that means daily sunscreen while you use it and for about a week after you stop.

How long until you notice a difference?

The thicker, firmer skin in the forearm study was measured after about 6 months of use, and the sun-sensitivity trial ran for 4 weeks.

How do you use glycolic acid?

Most people use it in the evening, on clean skin, then moisturizer, with sunscreen every morning. On the body, it is one of the options for rough, bumpy patches; see how to exfoliate your body without irritation. On toner pads, follow how to use toner pads.

Who should be careful with glycolic acid?

Anyone who spends long hours outdoors, has easily irritated skin, or already uses a retinoid should start slowly and add one active at a time, so that if skin stings you know which product caused it. Patch test a new acid before using it all over.