Stretch marks or striae (singular stria), as they are called in dermatology, are a form of scarring on the skin with an off-color hue. They are caused by tearing of the dermis and over time can diminish but not disappear completely. Stretch marks are often the result of the rapid stretching of the skin associated with rapid growth (common in puberty) or weight gain (e.g. pregnancy, muscle building, or rapid gain of fat) or in some cases, severe pulling force on skin that overcomes the dermis' elasticity.