Causes
They are often the result of stretching the skin in pregnancy or significant short term weight gain. When this is the cause it is sometimes called "Striae gravidarum".
Striae can also be caused by exercises. In this case muscle grows faster than your skin and surrounding tissue, thus leaving stretch marks.
Heavy or long-term corticosteroid use (cream or oral forms) can cause striae formation
It also can be one of many signs or symptoms of Cushing's syndrome.
Prevention and cure
Between 75 and 90 per cent of women develop stretch marks to some degree during pregnancy. The sustained stretching on the abdomen as a result of pregnancy usually means stretch marks may appear during the sixth or seventh month.
There are various methods that claim to remove them, including laser treatments, dermabrasion, and topical applications (e.g. cocoa butter), but none guarantees it.
There is no assured method of preventing stretch marks, although many believe that using oils or creams in high-risk areas may help prevent them by giving the skin more flexibility. Many over the counter products are sold for such use.
The only reliable treatment for already-existing stretch marks is surgery. While several topical applications exist, they are only effective in fading the stretch marks; they do not cause stretch marks to completely disappear.