Stretch marks, or striae, are scars created in the skin when it has stretched beyond its ability to recoil. The mark appears as a thin line that starts out red in color and fades to white. Stretch marks are partly hereditary, so if your mother has them, you're more likely to have them, too. But anything that causes the skin to stretch—obesity, puberty, rapid weight gain or loss, pregnancy, or even lifting weights and taking steroids—can cause striae.
To prevent stretch marks, keep your skin hydrated and healthy. Use an oil-based, thick moisturizer (like ShiKai's Borage Dry Skin Therapy) and drink six to eight 8-ounce glasses of water daily. Cocoa butter also has a reputation for preventing stretch marks, but there are no studies that show it works better than a regular moisturizer.
More aggressive treatments for stretch marks include topical retinoids like Renova, Retin-A, and Avita, which minimize scars by stimulating the production of collagen in the skin. Laser treatments have also been shown to lighten and smooth stretch marks. Vascular lasers, such as the Vbeam, which are typically used to treat birthmarks and rosacea, target the color red and are therefore useful when stretch marks first appear. The Fraxel laser, an infrared resurfacing laser, has been shown to stimulate collagen production, which helps fill in the sunken area beneath the older, white scars. Signs of improvement should be visible after three to six monthly treatments. (It's not cheap: One session can run from $600 to $1,200, depending on the size of the scar, and insurance rarely covers the procedure.)
Stretch marks are generally a cosmetic concern. If striae suddenly appear with other changes like facial hair, irregular menses, a swollen face, or diabetes, see your physician. This may indicate an underlying condition called Cushing's syndrome.
—Joely Kaufman, M.D., director of geriatrics and anti-aging at the University of Miami Cosmetic Center