A stretch mark on the skin is caused by too fast expansion of the body making the skin suffer from the pulling forces leading it to stretch. This happens with those gaining weight too quickly, those getting pregnant with huge extended bellies, those young children growing into teenagers with a quick change of the physical bodies. Besides, some Hormone changes can be another reason. The colors of the stretch vary from person to person like pink, red, brown, or white. But for the beginning stage, they usually look red or purple, which is easy to be treated.