Striae, commonly known as stretch marks are typically just a scarring of the skin that is a result of the tearing of the dermis naturally because of circumstances associating with rapid growth or rapid weight change. Any age group can have stretch marks, maybe because of puberty, hormonal changes, pregnancy etc. These marks can appear almost on any part of the body but mostly on areas that have large amounts of fat stored in them. When they start to appear for the first time, the affected area may start to feel wrinkly and in some cases slightly itchy as well. Striae have reddish to purplish hues which over time tend to lose color and fade away. But the areas that had the marks can feel soft on touching.

source: https://healthincenter.com/stretch-marks