Can cocoa butter or a store-bought cream claiming to prevent or fix those unwelcome post-pregnancy stretch marks make good on its promise?

Don't believe the hype.

"Few to none of the items touted to prevent or fix stretch marks really work," says Frank Wang, M.D., assistant professor and a dermatologist at the University of Michigan Health System. "Most of the existing products aren't based on solid scientific research."

Dermatologists, after all, are still learning about what causes stretch marks in the first place, Wang says.

The line-shaped lesions affect 50 to 90 percent of pregnant women — with some moms-to-be at a higher risk due to family history, the amount of weight gained during pregnancy and whether they're giving birth to multiples, among other factors.

The condition has received little attention from researchers because it isn't viewed as medically dangerous.

But for some, a deeper review warrants consideration.

"Stretch marks may compound the stress of new motherhood for many women," Wang says. "Some may feel like their self-esteem, quality of life and willingness to engage in certain activities, like swimming in a bathing suit, are affected."

Going skin-deep

In a study published last year in the British Journal of Dermatology, Wang and his team investigated what could be causing stretch marks at the molecular level.

Studying skin samples from 27 pregnant women who had recently formed stretch marks, they compared the stretch-marked skin to portions of nearby stretched skin on the abdomen and to less-stretched skin on the hip.

Wang and his colleagues determined that the skin's elastic fiber network — which gives skin the ability to "snap back" after stretching out — is disrupted when a stretch mark develops. The network remains disrupted after childbirth and, despite the body's efforts, isn't able to repair itself.

That, Wang says, promotes the lax, loose skin seen in more-mature stretch marks as a woman ages.

For now, remedial cures are scant. Present research of topical treatment options hasn't found anything to effectively repair those disrupted elastic fibers.

A proactive approach

Such an impasse could spur scientists to instead take a preventive approach.

"It may make more sense to focus on preserving the elastic fibers you have rather than repairing damaged ones within stretch marks," says Wang, who is continuing his research in part with a survey of 200 pregnant women to learn about how stretch marks affect their well-being.

One of his studies in the works examines changes in collagen — the structural protein that gives skin its strength and support — in stretch marks. Wang's team also is looking at changes in more-established stretch marks and why they remain, more or less, permanent over time. 

The authors see potential for expanding this knowledge to individuals affected by stretch marks in other ways. Among them: obesity, growth spurts or steroid usage.

Still, it will take time for researchers to target a way to prevent stretch marks at the source.

Says Wang: "It's more complicated than just rubbing something on your stomach."

The research was funded in part by a Dermatology Foundation Research Fellowship to Wang.