What causes stretch marks?

Stretch marks are commonly seen in children during growth spurts or in women who are pregnant. When the body gains weight quickly, there is a shearing or stretching of the skin leaving stretch marks. Stretch marks can appear on the breasts, abdomen, hips and thighs. No amount of cocoa butter, moisturizer or vitamin E will prevent stretch marks. When they first appear they are pink or red streaks but with time they fade to white becoming far less noticeable. Topical retinoid creams and lasers can be used diminish the appearance.

Stretch marks or striae, are lesions that tend to form in the dermis during periods of hormonal flux, with weight gain or loss, pregnancy, and other periods of hormone change. When the body's elastic fibers deep beneath the epidermis becomes damaged these scars can appear. Women often tend to get them on their breasts, thighs, hips, abdomen, arms, around the belly button, buttocks and back.

In addition to genetics, sagging skin around our torso and lower extremities is usually attributed to extreme weight fluctuations and diminished muscle mass. Excessive weight changes will break or weaken the supportive elastin fibers in our dermis, resulting in stretch marks. Once this occurs, the tensile strength within the dermis is lost and the skin cannot bounce back and restore its original shape. This is similar to when a rubber band is stretched beyond its limit and remains weakened. If the weight loss is accompanied with loss of muscle mass, there will be a concurrent loss of tone and your body will appear flaccid.

Stretching of the skin during weight gain and loss leads to stretch mark formation. There is permanent breakage of the cells and fibers of the skin. Up to 90% of women may be affected by the cracking of the skin during expansion from pregnancy leading to permanent stretch marks. It is also known as "striae distensae". Prevention is mostly avoiding quick weight gain and then loss. Interestingly, the appearance of the marks depends on the color of your skin. The marks may start out pink or red and then fade to white after a year. The thinning of the skin remains permanent. Applying moisturizers several times a day prior to tissue expansion (pregnancy, breast implant surgery) may greatly reduce incidence of stretch marks. 

These scars form when skin has lost the integrity and strong structure beneath it. Abnormal architecture of the collagen and elastin fibers in the dermis is the crux of the problem. During pregnancy the problem is twofold, since the skin is also stretched to the limit and doesn't return to its original, tight elasticity. Ultimately, stretch marks are genetic, so it's not true that only overweight or pregnant women get them. I've seen young women and those with model-thin physiques with them. Men get stretch marks (and steroid supplements increase the risk), and a lot of adolescents get them when hormones kick in and they have growth spurts. Though there's no typical stretch mark patient, rapid weight loss and gain are big factors.