What Causes Rashes At The Rear End Of Hips?

Hi, my friend is 31 5'4" and pretty good health. She has a rash on her rear end on her hips. It is speckled, not inflamed and the actual rash marks looks like they were once scabs and now there is no scabs so they look hollow. But I asked her if she scratched them, she said she never scratched them or even knew it was there, until she was in the shower. And it is only a small patch it hasn't spread and doesn't look like it is starting to spread