Detailed answer

Stretch marks, also known as striae, can occur on the thighs. They are caused by rapid stretching of the skin, which can happen during weight gain, growth spurts, pregnancy, or muscle building. The stretching causes the middle layer of the skin, called the dermis, to tear, resulting in the appearance of stretch marks. The thighs are a common area for stretch marks to develop due to the natural fluctuations in body weight and growth that often occur in this region. While stretch marks are not harmful, many people seek treatment options to reduce their visibility.