when in doubt, throw it out

When you keep dabbing from the same cosmetics, and a horrific rash blooms on your face meat, don't come crying to me.

Microbe growth in makeup can cause skin irritations and infections, explains Paula Begoun, the author of "Don't Go to the Cosmetics Counter Without Me." The worst offenders are liquid cosmetics, which build up bacteria more quickly. Keep mascara for a maximum of three months; other liquids and creams (eyeliner, foundation) for no more than a year. Powders (eye shadow, blush) can be used safely for up to two years.

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