I can't give a lot of details because I don't have many. Approximately 6 months, recently fixed and vaccinated, cat that was indoor/outdoor with a cat hoarder.
My guess is either mange or scabies.
Although the root cause is different, there's some overlap between the two. In fact, some people call them the same thing.
Either way, a trip to the vet is in order. Given proper treatment, you should be able to clear this up in a reasonable time.