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Your guide to decoding the latest skincare ingredients:

Probiotics
You may include these "friendly" bacteria in your diet to regulate your GI tract; some beauty companies now suggest you also put them on your face to improve your skin. Most dermatologists, however, find the idea hard to digest. Some studies have shown that probiotics can soothe inflamed skin in children—but only when taken orally.

Growth Factors
Proteins that promote cell growth, these molecules could theoretically grow you fresh, smooth skin. In reality, no independent studies have shown that a skin cream with growth factors can improve your complexion, says molecular biologist Yann Echelard, PhD: "These are large, fragile molecules unlikely to penetrate your skin in the concentrations included in cosmetics."

Stem Cells
Human stem cells have awesome regenerative potential. But you won't find them in a face cream. What you may find: stem cells derived from anything from apples to rice. "Those stem cells have no relevance to human skin," says Ron Moy, MD, clinical professor of dermatology at UCLA.