Vitamin C

Few topical vitamins have as much research behind them as vitamin C. Used consistently, it can visibly ease several signs of aging at once, thinning skin, loss of firmness, fine lines, and wrinkles, while also brightening an uneven complexion and helping repair and calm the skin.

Its collagen building power comes down to a very specific biological role. Vitamin C acts as a required cofactor for prolyl and lysyl hydroxylase, two enzymes the skin needs to properly assemble collagen. Without enough vitamin C on hand, these enzymes can't do their job, which is part of why adequate vitamin C levels are so closely tied to firmer, more resilient looking skin over time. Separately, its antioxidant activity works by neutralizing free radicals through electron transfer, which helps prevent the kind of cellular damage that drives visible photoaging.

Skincare products use vitamin C in several different forms. Ascorbic acid, also called L ascorbic acid, is the most studied and has the strongest evidence for effectiveness, though you'll also see magnesium ascorbyl phosphate, tetrahexyldecyl ascorbate, ascorbyl palmitate, ascorbyl glucosamine, and ascorbyl tetraisopalmitate on ingredient lists.