What commonly causes stretch marks on the skin?

Stretch marks, also known as striae, are primarily caused by the rapid stretching of the skin that occurs during periods of rapid growth or significant changes in body size. This can happen during adolescence when individuals experience growth spurts, during pregnancy as the skin expands to accommodate a growing fetus, or when there are rapid weight gains or losses.

When the skin stretches quickly, the underlying collagen and elastin fibers may not be able to keep up with the demand, leading to breaks in the tissue that manifest as stretch marks. These marks often begin as red, purple, or dark brown streaks and can fade to a lighter color over time.

While factors like sun damage, aging, and genetics can influence skin texture and elasticity, the immediate cause of stretch marks is specifically linked to the skin undergoing rapid expansion beyond its usual limits. Understanding this mechanism helps in recognizing why certain life stages and body changes are associated with the appearance of stretch marks.