Stretch marks or striae, are a form of scarring on the skin with an off-color hue. They are caused by tearing of the dermis, which over time may diminish, but will not disappear completely.
Stretch marks are often the result of the rapid stretching of the skin associated with rapid growth or rapid weight changes. Stretch marks may also be influenced by hormonal changes associated with puberty, pregnancy, bodybuilding, hormone replacement therapy, etc. (adapted from Wikipedia)
Image source: planningdoesntwork.wordpress.com (link)
The image above shows stretch marks following pregnancy. Between 75% and 90% of women develop stretch marks to some degree during pregnancy.Other similar posts