There are many old wives’ tales about stretch marks—and how to prevent or erase them. (Ever slather your pregnant belly with cocoa butter?) The truth is, there’s no way to avoid them entirely. But you can make the marks you have less visible.
 

What Causes Them?

"Stretch marks are scars that can form when collagen and elastin fibers tear during puberty, pregnancy, or significant weight gain or loss that occurs in a short period of time," says New York City dermatologist Francesca Fusco. But they aren’t simply the result of skin overstretching, as is often thought. "During puberty, pregnancy, and weight changes, elevated levels of hormones called glucocorticoids are produced by the adrenal glands," says Zoe Diana Draelos, a consulting professor of dermatology at the Duke University School of Medicine, in Durham, North Carolina. Those hormones are what can cause the collagen and elastin fibers to tear when the skin is stretched. "Weight gain itself doesn’t cause stretch marks—it promotes the hormonal changes that cause them," says Draelos. Doctors agree that you can’t prevent marks (so forget about that cocoa butter). Rather, "genetics play a big role in whether someone gets them," says New York City dermatologist Bruce Katz.