Scaly skin on back near tail

I rescued to kittens the day after they were born. They are 5 weeks old now and are doing very well. Today while massaging them, I noticed they both have some dry scaly skin on their backs near their tails. Any suggestions on what it could be and how I can treat it? They have an appointment wtih the vet in a week, should they be seen before then. They are both eating and drinking well. when they were very young, I would wash them with a damp wash cloth after each feeding. If they were particularly messy, I would wash them in lukewarm water with baby shampoo and then wrap them to keep them warm. is it possible i washed them to much?

Any advise is appreciated

thank you!

I don`t know what it is but Kitty has the same thing. He always has.
Our first vet said it was because I didn`t brush him enough but even if I brush him every day it`s still there and I have never bathed him, I don`t want to die!

Our new vet looked because he began pulling the hair out there but as it was growing back he didn`t do any tests. He seemed to think it was a stress thing and wanted to put him on Prozac then the next time he gave him some steroids and it`s a lot better but still a bit flakey.

Sooooo, it could be many things. Diet, shampoo residue, allergy, fleas...