Stretch marks are bands of scar tissue that occurs when your skin is stretched or shrunk too quickly, not allowing your skin enough time to grow or contract leading to injury and the formation of the scar.

Common causes of stretch marks include:

  • Puberty growth spurts
  • Pregnancy
  • Rapid muscle growth when bodybuilding
  • Weight gain or loss

Your hormones and heredity may also play a role in your development of stretch marks.