During puberty, pregnancy, or even weight gain, skin can become stretched to a point where it does not bounce back. As a result, stretch marks, or striae, form. These marks first appear as pink, red, or purple, streaks across the skin in common areas including the abdomen, thighs, hips, breasts, upper arms, or lower back. Over time, the stretch marks fade and the streaks change to a glossy silver or white color.
Stretch marks occur in the middle layer of the skin, or dermis. This layer of skin contains elastin and collagen, which are responsible for helping skin maintain its shape. However, with constant stretching, the collagen and elastin break down leaving behind stretch marks.