Anyone who has wrestled with adolescent acne will remember how difficult it can be to eradicate. Cats are often afflicted with a similar condition, called feline acne -- more commonly known as chin acne or kitty acne.
Like acne in humans, its causes can vary, including food allergies, contact allergies, and possibly stress.
Sources
Plastic food dishes have long been suspected as a culprit in chin acne. Plastic is a magnet for bacteria and dirt that work their way into scratches and nicks, reinfecting your cat and/or spreading bacteria to other cats in the household. Veterinarians and other feline experts recommend using only glass or metal food bowls, and daily washing of those, in order to help prevent this common condition.
It has been my experience that the hard plastic-like containers of automatic water fountains do not scratch, and I have never heard of one causing kitty acne. Still, they should be routinely cleaned according to the manufacturers' recommendations.
Treatment
Stress-related acne can be treated by finding the causes of the stress and eliminating or ameliorating them, if possible. Emotionally-induced stress may be relieved by medication, or pheromone-based products, such as Feliway. Environmentally-caused stress might be solved by doing whatever possible to change the environment (providing plenty of toys and vertical space, move the furniture back that you just moved, or backing off and gradually re-introducing that new cat or dog).
Appearance
Feline acne starts as small, oily black plugs in the chin, much like blackheads, which may progress to red, itchy bumps, which may become infected. Treatment varies, but most veterinarians will recommend daily cleaning with an antiseptic soap, followed by a topical ointment, either antibiotic or anti-fungal. Oral antibiotics may also be prescribed.
Severe cases of feline acne may be difficult to eradicate, so you'll want to take your cat to the veterinarian at the first sign of black spots on the chin. Although cats are not embarrassed by acne, as humans are, the condition is still potentially serious and can result in infections, painful swelling, and scaring, and should not be ignored.
Disclaimer
When a cat is ill, your veterinarian should always be your first resource. This article is meant only to give you a starting place to do your own research on the topic so you can make an informed decision should it ever become necessary.