Kona also gets feline acne on her chin. Hers started when we adopted her dog-sister, when Kona was 7. Perhaps that lends credability to stress and overactive/clogged scent glands as causes.

We visited the vet when it first appeared, as I was terrified she had chin tumors or something. Since they were just pimples thankfully, he suggested warm compresses as a first treatment. She is much better now, just an occasional pimple so minor that it heals itself. Good luck to Pepper.