Vitabiotics-Pregnacare Cream (100ml)Stretch marks can appear anywhere on the body where the skin has been stretched. They occur when the lower layer of the skin containing collagen and elastin, which give our skin its elasticity, becomes damaged by a rapid weight loss or weight gain, such as in pregnancy. The purple appearance of the stretch mark on the skin is caused by the small blood vessels beneath the surface, which become more visible with stretching.