What people believe
The skincare industry has built a substantial market around the idea that rubbing cocoa butter, bio-oil, or other topical products on your skin during pregnancy will prevent stretch marks.
What the evidence says
A Cochrane Review of topical treatments for stretch marks in pregnancy examined randomised controlled trials of cocoa butter, olive oil, vitamin E cream, and other preparations. The conclusion: no topical product has been reliably shown to prevent stretch marks.1
Stretch marks (striae gravidarum) are caused by the stretching and tearing of the dermis combined with hormonal changes that alter the structure of collagen and elastin fibres.2 The primary risk factors are genetic predisposition, the degree and speed of skin stretching, maternal age, and pre-pregnancy BMI. Whether you get stretch marks is primarily determined by your genetics — not by what you rub on your skin.
What to do instead
The single most evidence-supported factor is rate of weight gain. Steady, gradual weight gain within the ACOG-recommended range is the closest thing to a modifiable factor.3 Keeping skin hydrated is reasonable for comfort, but choose any basic moisturiser. Stretch marks typically fade significantly in the months and years after delivery.