You thought you were in the clear back in high school when you finally got your hormonal acne under control. But your hormones might once again be wreaking havoc on your skin. Fluctuating levels can cause brown spots, dryness, lines, and sagging skin. "Hormones play an integral role in skin aging," says Heidi Waldorf, M.D., a dermatologist in New York City. "If you ask anyone who has gone through menopause or even perimenopause, she'll tell you that her skin is suddenly older," she says. "Estrogen is really the biggie here." Here are some of the ways its highs and lows affect your skin -- and how you can ward off its aging effects.