In medicine (see also dermatology), striae are most commonly seen as stretch marks on the skin with a silvery white hue.
Striae can also be caused by exercises. In this case your muscles grow faster than your skin, thus leaving white 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.
A few ways to minimize striae is by keeping skin elasticity as high as possible by using a skin moisturizer on a regular basis.