What Are Those Ingredients in Your Skin-Care Products?

Alpha Lipoic Acid

Also known as: Lipoic acid.

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

What it treats: Sun damage, aging.

How it works: Alpha lipoic acid "helps with exfoliation and the stimulation of collagen, which may lead to a smoother appearance of the skin," says Ronald R. Brancaccio, a clinical professor of dermatology at the New York University School of Medicine, in New York City. Since it's a powerful exfoliator, avoid it if your skin is sensitive or prone to redness.

RS picks: N.V. Perricone M.D. Advanced Eye Area Therapy, $95, perriconemd.com. Aubrey Organics Rosa Mosqueta Night Creme, $23.50, aubrey-organics.com.