I don't know if or how serious this is, but iv had a older rat have this same thing wrong with her, and eventually the dry skin turned into lots of scabs and she was practically a naked by the time she died & meds the vets gave us... never worked. Vince is about a yr and a half maybe, he is fairly lazy, and a bit more on the chubby side but has always been his whole life. There is vertualli no hair in this spot and his skin looks dry & flaky, there is no scabs, but his hair used to be awfully thick, and latly its seemed really thin. It also looks like he has lost some weight. The vet didnt know what was wrong with Dot(my girl who had this worse) he assumed it was fleas but... there wasnt any n just didnt know. But put her on meds anyways for a bacterial infection. He lives with 6 other rattie siblings, and nobody else has this problem. William does have little scabs all over his body, but i assume its mainly because he does like to play rough with one of the roudy girls, and it couldnt b fleas because everyone else would have it. Vince spends most of his time sleeping, they do go outside every once in a while. Iv put some moisturizer stuff on that spot just to keep it from becomeing to dry. I feed them all regular rat food(pre-stige by versa-laga) they get the occational dog & cat treats & sometimes get the higher brand dog or cat food mixed in with their food to give them some variety but its more rat food then the other. They get fruits and veggies every so often also. Please dont just tell me to take him to the vets, id like to have an idea of w.e it may be if i need to take him to the vets so i can give them suggestions