My rat's skin is bloody: what's wrong?

this is going to sound terrible, but I've been so concerned with my rat dying of a tumor that I JUST noticed that my other rat has an awful skin condition. all of her skin from her neck down is raw and bloody, with patches of hair missing. I don't see any bugs or anything, and the other rat doesn't seem to have this. What is it/ is it treatable? Is there anything I can do to help her? I was thinking a bath, but that might just hurt. Thanks!