What Are Those Ingredients in Your Skin-Care Products?

Dermatologists give a crash course on what goes into skin-care products.

Vitamin C

Also known as: Ascorbic acid, L-ascorbic acid, ascorbate, magnesium ascorbyl phosphate, ascorbyl palmitate.

Good for: All skin types, except very sensitive skin.

What it treats: Sun damage, aging.

How it works: Vitamin C neutralizes free radicals, which form when the skin is exposed to sun, pollution, cigarette smoke, and other harmful elements. Free radicals damage collagen deep within the skin, causing wrinkles, blotches, and inflammation.

RS picks: Dr. Brandt "C" Gel, $90, dermstore.com. Cellex-C High Potency Serum, $90, drugstore.com.