Stretch marks or striae, as they are called in dermatology, are a form of scarring on the skin with a silvery white hue. They are caused by tearing of the dermis, and over time can diminish but not disappear completely. Stretch marks are generally associated with pregnancy, obesity, and can develop during rapid muscle growth from body building. Stretch marks are the result of the rapid stretching of the skin associated with rapid growth (e.g. puberty) or weight gain (e.g. pregnancy), and anabolic steroid use. Although the skin is fairly elastic, rapid stretching of the skin will leave permanent stretch marks.
Stretch marks (also referred to as striae distensae. Medical terminology for these kinds of markings include striae atrophicae, vergetures, striae cutis distensae, striae gravidarum (in cases where it is caused by pregnancy), lineae atrophicae, striae distensae, linea albicante, or simply striae.