StriaeStretch marks form during rapid growth of the body, such as during puberty or pregnancy. In pregnancy, they usually form during the last trimester, and usually on the belly. They also commonly occur on the breasts, thighs, hips, lower back and buttocks. These are known as striae gravidarum.
Stretch marks are caused by tearing of the dermis. This is often from the rapid stretching of the skin associated with rapid growth or rapid weight changes. Stretch marks may also be influenced by hormonal changes associated with puberty, pregnancy, bodybuilding, or hormone replacement therapy.
There is no evidence that creams used during pregnancy prevent stretch marks. Once they have formed there is no clearly effective treatment, though various methods have been attempted and studied.