Stretch marks, or striae, are visible lines that form when the skin stretches too quickly and the underlying collagen and elastin fibers break. They often appear on the abdomen, thighs, hips, breasts, or arms. These marks may start out red or purple and gradually fade to white or silver over time. Although they are not medically dangerous, many people choose to treat them to improve the appearance and texture of their skin. Stretch marks can be a cosmetic concern that affects self-confidence.