No, but if you're a true beauty junkie, the sheer amount of stuff you use may make a skin issue worse! Applying several products that have the same goal can overwhelm your skin, says Robert Guida, M.D., a facial plastic surgeon in New York City. This is particularly true with antiaging formulas. Using retinol (for fine lines) or hydroquinone (to lessen dark spots) on top of something else with strong exfoliating effects (like glycolic acid) can cause irritation, dryness or even a mild burn, Dr. Guida warns. (Overdoing the acne fighters can be bad for skin, too, he says.) Committing to one brand's line is an easy way to play it safe. The system is developed to work together. Devoted to diversification? Leave three days between doses of creams that exfoliate, lighten pigment or combat pimples. That way, you can play the field productwise but be loyal to the cause of good skin.