I don't have a solution,but I have a cat with the same problem. My cat Whisper has a dandruff butt,too. I try to brush her, it only makes it worse. It doesn't seem to be spreading or causing her any concern or injuring her skin,so I ignore it. Next time I go to the vet,I"ll ask about it.

I've had cats with this problem, too. A Persian I had not only had 'dry butt', he had 'stud tail'(a build-up of oil) just a couple inches away on top of his tail. Adding EFA's(omega oils) to his food helped the dry patch(it took a while), but he always had the stud tail. You might try rubbing some oil, maybe olive oil, into the dry skin after you've brushed some of the flakes away. I did this to break up my cat's stud tail before bathing him, but I don't know why it wouldn't work just to rub some in and leave it. I've seen dogs with this problem too. Just my guess, but I think it's a spot they can't easily groom for themselves. Good luck, and let us know if you find something that works.

My Persian, Simba has this problem, seems to get it every late fall, into winter...It gets so bad, he has a bald spot there...He also has the oil problem the previous poster wrote about...I feel so bad for him, but the vet said he's fine, it's just dry skin...I will try putting the EFAs in his food....

Im gonna bath her problem is she freaks out an she gain so much weight after i got her fixed. So im gonna try bathing her an i no she will go nuts so i have to put armer on lol her skin is so dry im actually gonna try head an shoulders. Il let you no what happen. Ive tried changing her food im just at a loss.