Glycolic acid

It exfoliates. Glycolic acid is an alpha hydroxy acid that loosens the bonds holding dead cells to the surface, so they shed more easily. Used consistently, that can mean smoother texture and brighter-looking skin. It does not add moisture, and overdoing it can leave skin red, tight and stingy, which is the opposite of the goal.

Most people do best at night, on clean, dry skin, starting once or twice a week. Night use is not a hard rule, but it keeps the acid away from midday sun, and your skin is more sun-sensitive afterward. Whatever time you pick, wear sunscreen the next morning. Build up slowly if your skin tolerates it.

No, and the similar names cause real confusion. Glycolic acid is an exfoliating acid that can sting. Glycerin is a humectant that pulls water into skin and is generally very gentle. They can sit happily in the same product, but swapping one for the other will not get you the result you expect.

No. Both are alpha hydroxy acids, but glycolic acid has a smaller molecule, which is generally thought to be why it feels stronger and irritates more easily. Lactic acid is larger and usually reads as gentler, so it is a common pick for sensitive skin. Both exfoliate; neither is automatically better for you.

A mild tingle can be normal, but real burning means something is off. Common causes are too high a strength, too frequent use, a damaged skin barrier, or stacking it with retinoids and other actives. Rinse it off, skip a few days, and drop to a gentler schedule. Persistent pain or swelling is a reason to see a clinician.