Stretch marks are caused by the continuous pulling and stretching of the skin as time goes on.
Stretch marks are often brought on by pregnancy, amidst puberty and when undergoing hormonal changes. They appear as stripes or “streaks” in the skin that are long, narrow and sometimes unsightly, but otherwise harmless. Some fade over time, while others are much more stubborn; usually this is determined by how intense the rapid stretching of the area was in addition to its duration.