I did some quick googling and it appears to be mostly related to bone structure and as I suspected, childbirth (widening of the hips) can pronounce it. Have you had kids? Of course, the thinner someone gets the easier it is to get one. I don't know if my running (toning of thighs) has contributed to it?? But its nice. I like not having chub rub! lol...and my legs look long, lean and sexy (in pants lol) I think is helps balance out curvy hips, which I have. Enjoy it!!! So many women wish their thighs didn't rub together while walking.