losing hair

Hi,

My cat Jake has small patches of his fur missing on both of his sides.
Missing may be a bad description, I would say the fur looks thin, if
that makes sense to anyone...

I am bringing him in tomorrow morning to have the vet take a look, as
I cannot tell if this is serious or not.

Any ideas what this could be?

I was thinking maybe he was shedding, but there seems to be too much
fur missing for that. e gets upset if I try to pet him there, and
tries to bite me. Does this sound serious enough to rush him in
somewhere? He acts pretty normal otherwise, very playful, good
appetite, etc.


Justin - worried