Stretch marks, or scars that happen when your skin rapidly stretches or shrinks, typically show up as bands of lines running across your skin.

Stretch marks are very common — estimates suggest up to 90 percent of people have them. They commonly appear during or after pregnancy, or after other sudden or rapid changes in your weight. For example, rapidly growing adolescentsTrusted Source might notice some stretch marks.

These marks can appear just about anywhere, but they’re most common on your:

• stomach
• breasts
• upper arms
• thighs
• buttocks