Oh, I don't know. Vet, maybe?

My cat has a lump in his neck which goes up and down.  The vet said it was
probably a cyst that drains out every so often.  The vet had a good feel
around and couldn't find any connection to the underlying muscle so it's
effectively just floating in the skin.  He said its probably nothing to
worry about, and didn't see the need to remove it as that would probably be
more risky to put the cat under anaesthetic than leaving the lump there.

Cats can still get acne even if they are not drinking & eating from plastic
bowls.  I have a Tom who is a very sloppy eater & drinker and gets himself
messy on the chin.  If one of the other cats doesn't groom him there he gets
acne.  I've just taken to wiping his chin off every evening with a warm wet
paper towel to keep it from developing.

This could very well be acne but you should still take him to the vet to
have it looked at.

Celeste