Stretch marks, or striae as they are also called, are very common and occur when the skin is stretched out quickly. It is common to develop stretch marks during puberty, as the body grows rapidly and the skin does not have time to adjust. For girls in puberty, common areas are hips and thighs, while boys often get striae on the back and shoulders. Pregnancy is also a common cause of stretch marks on your stomach and sometimes your breasts. Stretch marks can initially be dark and red, while older stretch marks are often lighter than the surrounding skin.
Stretch marks often fade over time but can also be treated with softening and exfoliating products. By moisturising and softening the skin regularly, you can help prevent stretch marks. It is also important that you protect the skin from the sun to avoid pigmentation, as the skin around and on the stretches - especially when they are new - is somewhat more sensitive.