Stretch Marks also know as striae or striae distension, are a form of scarring on the skin with off-colour hue. Over time they may diminish, but will not disappear completely. Stretch marks are caused by tearing of the dermis during periods of rapid growth of the body, such as during puberty, pregnancy, weight gain or rapid weight loss. Stretch marks are stripes on the skin especially on the abdomen, caused by distension of the skin.