Stretch marks, also known as striae, are long, narrow streaks, stripes or lines that appear on the skin as a result of rapid stretching or expansion of the skin.
They are a form of scarring that occurs when the skin is stretched beyond its natural capacity and the underlying collagen and elastin fibers are damaged.
Stretch marks can occur on various parts of the body, including the abdomen, thighs, hips, buttocks, breasts, upper arms, and lower back. They are more common in women than men and can develop during pregnancy, puberty, weight gain, or rapid muscle growth.
Initially, stretch marks may appear as raised or reddish-purple lines, but over time they often fade to a lighter color and become less noticeable. While stretch marks are not harmful, they can be a cosmetic concern for some people.