There are all kinds of fungi it could be or an allergy. I would take him in.
the vet will be able to do a scrape. My one cat had what looked like
ringworm when her hair started coming off her ear. It came back negative on
that, but we used the same topical treatment and it came back. I figure I
brought something home from the barn I ride at or something. Had a long
haired cat when I was young that lost a bunch of hair in spots and no
scaling. The vet gave us a certain shampoo and we had to bathe her twice a
week for a few weeks. Came back fine and never happened again.  I would sure
get it looked at.

I don't, but if you take him to the vet, I imagine that he/she will have an
idea.