Help Needed! Skin reaction to shampoo?

[ezap44]

I think knuckles may have a skin reaction to a bath he got on Sunday. He has little bumps all over his sides! They don't seem to bother him too much but are big enough to be viewable and when touched are irritating to him. I've bathed him 2 times with oatmeal shampoo from the vet and given him benadryl. Any other recommendations?!