If you get red gunk out of the ears, it is mites, if not, is it round and spreading, if so, could be fungus, or ringworm,
Could be a bite or sting, what I do know, being involved with veternarians and shelter animals for 20 years, cats, get infections sooner than dogs, it should be attended to, it will infiltrate, and that will
cost more money, the cat most likely has an infection, which require antibiotics, and or if mites, ivomec, which I put in my cat's ears. Or, you can get a once a month pill that kills heartworm, fleas, and mites oh and I think, ticks. But, once again, cats get infections more easily than dogs, I would hate to see a scenario, that, it becomes more inflamed fills up with water and has to be lances surgically and then, a drain is left in.
Or as someone said, it could be food,