| Credit: Rita Maas

Also known as: 4-hydroxy-3-methoxycinnamic acid.
Good for:
Dry skin, normal skin.
What it treats:
Sun damage, aging.
How it works:
Usually combined with vitamins C and E, "ferulic acid helps stabilize them," says Barbara R. Reed, a clinical professor of dermatology at the University of Colorado Health Science Center, in Denver. This doubles their power as sun-protective agents and boosts their ability to neutralize free radicals.
 pick: SkinCeuticals CE Ferulic serum, $135, for store locations.