Stretch marks seem to be caused, literally, by a stretching of the skin. Stretch marks are more extreme when coupled with an increase in cortisone, a hormone produced by the adrenal glands. Cortisone weakens elastic fibers in the skin.
Stretch marks develop in a variety of circumstances, including: Pregnancy. Most pregnant women develop stretch marks by the end of their pregnancy. The physical stretching of the skin, along with hormonal factors, likely plays a role. Weight gain. Stretch marks sometimes occur during substantial weight gain. Weightlifters can develop stretch marks, particularly on the arms. Adolescents may notice stretch marks during growth spurts. Medication use. Corticosteroid creams, lotions and pills and chronic use of oral or systemic steroids can cause stretch marks. Conditions or diseases. Cushing's syndrome and adrenal gland diseases can cause widespread stretch marks, as can Marfan syndrome, Ehlers-Danlos syndrome and other hereditary (genetic) disorders.
From gaining weight. This happens when you gain weight in your thighs and stomach and such. It often happens to pregnant women. They are called stretch marks because they are marks from where your skin has tried to stretch too fast from more weight.
I thought cause you grow faster than normal like if you get really fat fast. if there pink you can get rid of them by putting on lotion every day on that spot but if there almost your skin color its there forever