It's actually genetic. The skins elastin is what causes them. Some people have less elastin and therefore they get stretch marks easier. Using products can help, but if you have skin that is prone to them, then you will get them no matter how often u bathe in cream! Trust me. WIth my first, I lathered myself morning and night and I had purple marks everywhere. I called myself the purple zebra. With jess, not many and this time. None. But only because my skin had stretched this much before so....