Stretch marks don't occur because of weight gain they occur because of weight loss. And by weight loss I don't mean a drastic loss. People who constantly gain and lose weight on and off tend to get stretch marks. When there is excess fat the skin stretches to accomodate the fat... that causes a tear in the dermis and when the body looses slight weight or drastically looses weight (either one) the tear appears as a stretch mark. The skin tear is unfortunately permanent... it is red when it is fresh and tends to fade away to skin color (the tear remains as is only the color fades). So try to remain at a steady weight according to your height. This will prevent further marks. Prevention is the only way to assure new ones don't come up.