May I ask, how old is your cat?
Male or female?
Does he go outside?
Are there any other sores on the rest of his body?
Thanks for the information. I'm writing a reply now and will send it shortly.
Hello again, I suspect your cat has a condition known as cat chin acne. The cause of this is not entirely certain, but may be related to allergy, poor grooming, excess skin oils, or suppressed immune system.
You have a couple of options here. One is a visit to your vet for an exam, and to rule out other skin conditions, such as ringworm (a fungal infection) or mites. That's always a good idea. However, I also think it would be fine to treat this at home first. It may resolve without medical care.
First, if you use any plastic food or water dishes, replace with stainless steel or smooth ceramic. Plastic holds bacteria, and in addition, it can be allergenic.
Second, treat the affected area as follows: I recommend Pyoben shampoo, available online. Gently wash the chin twice daily with this, and rinse well. Blot dry.
Third, try a fatty acid supplement. These are recommended for nearly all feline skin problems.
I hope this was helpful. Please feel free to ask any follow up questions you have. I would be happy to talk further with you.
Cats can get the mites which cause sarcoptic mange and notoedric mange. These are diagnosed with a skin scraping. Ear mites are a different species, and normally live in the ear canal. However, occasionally ear mites do spread to the skin around the ears.
It's possible one of these mites is ocurring with your cat. If he is very itchy, I would be more suspicious of mites. If he's not itchy, I still think chin acne is likely. The acne sometimes presents as a sore, like your boy has.
As a precaution against mites, apply a dose of Revolution to the back of his neck. This is a safe and effective treatment against ear mites and fleas. It's available from your vet or online. If he has a mange mite, he will need veterinary treatment.
Regarding his ears- cats with ear mites typically are itchy, and have a dark discharge like coffee grounds. Your vet can diagnose this by using the otiscope, or looking at a sample of the exudate under the microscope. Itchy ear can also mean simply a waxy buildup, or a yeast infection.
To sum up, to diagnose the mites for certain, bring him to your vet for an examination +/- skin scraping. If he's itchy, treating him with Revolution is fine to try first. I would also do the cleaning routine with the Pyoben shampoo in any case.
I will be here through the day if you have further questions. I appreciate your patience with the process.