Pretty much everyone is going to get stretch marks at some point (estimates of the marks' prevalence range from 50 to 80%), but we know surprisingly little about the way they form. However, new research gives us an up-close and personal look at the way our skin is changing when those lines appear. The study, published online recently in the British Journal of Dermatology, examined the way pregnancy stretch marks (technical term: "striae gravidarum") actually form on our skin at the molecular level. The researchers took samples from the stretch marks and surrounding skin of 27 pregnant women and checked them out using 3-D imaging. They found that, as you might suspect, pregnancy disrupts the stretchy network of fibers in your skin (which you can see in an amazing 3-D video below). Normally, the elasticity of these fibers is what allows your skin to snap back into place if you stretch it, but your body isn't able to repair them after they've been disrupted like this. And, what's more, the study authors say many of the products out there claiming to make stretch marks disappear aren't actually targeting this root cause. "Because stretch marks may compound the stress of new motherhood for many women, it's important to learn more about them," Frank Wang, MD, the study's lead author, said in a press release. "Some women feel like their self-esteem, quality of life and willingness to engage in certain activities are affected." Indeed, as we've written before, we aren't always prepared for the way our bodies change during and after pregnancy, and stretch marks may come as an unwelcome surprise. But, as this study proves, they are a totally normal part of many totally normal processes, including just growing up. So we say embrace your tiger stripes.