In one cat group I belong to, there has been some recent discussion about feline acne and how to treat it. The problem I see is most of cat owners and some vets don't distinguish between a cat with a dirty chin (henceforth called 'chin crud') and true feline acne. The treatments are similar but not identical.
So, what are the differences?
Chin crud is often the build up bacteria and food particles on the hair of the chin. A cat eats, gets a bit of food on the chin, and because the chin is hard to clean, the dirt allows bacteria to grow. Over time, the bacteria creates blackish residue on the hair. But, and this is key, the black crud is on the hair, above the skin, and not in the skin.
Since it's on the hair, this black crud can be washed off, usually with just water in a minute or two. If there is
more fat in the food, a bit of isopropyl alcohol and/or soap will help quickly remove it. Because it is bits of food and moisture mixed in with saliva to create black crud, it may stain white hair.
Wendy has this because her tongue hangs out, soaking her chin in saliva. I use a flea comb to comb off the bigger pieces and then a cosmetic pad with saline for contacts to wash it. Then I use EyeEnvy liquid and powder on the area. If I do this ever 2-3 days, her chin will be spotless. (Unfortunately, I often skip it during the week because I have such limited time.)
Feline acne is like human acne -- it is an infection in the skin. The skin usually develops blackheads first. The black areas are in the upper layer of the skin, as in the photo at the right. Over time, some of these blackheads lead to pimples (or zits of pustules of infection -- which ever is your favorite term) which erupt from the skin. The chin feels lumpy when rubbed. Interestingly, the 3 cats I have had with feline acne had perfectly clean chin hair, as can be seen in the photo at the right and the one below.
When James, Clancy, and Tolstoy developed this, I would express the pimples and then wash the chin with a dilute mixture of goldenseal extract. The goldenseal has a natural antibiotic property, but it also stains the hair yellow. (I could live with yellow chinned cats.) Once I figured out the source of the problem, it took about 3 weeks for it to clear up.
So why is there a confusion? Basically it comes down to careful observation and lack of distinction. Most owners and some vets see the black crud and immediately call it feline acne. They don't stop and determine it the problem is above or in the skin. Then they treat it with antibacterial soap and it clears up -- not because it was acne, but because the soap killed the bacteria on the hair.
To some, this is splitting hairs. (Sorry, I couldn't resist.) The problem is once the owner stops the using the antibacterial soap and the crud comes back, often the vet then uses antibiotics. I'm not a fan of antibiotics in general, and in this case, they usually won't work, so then the vet tries either stronger antibiotics or suggests steroids. It comes down to treating a cat with some serious drugs for a problem the cat really doesn't have!
So where does chin crud and feline acne come from? The most commonly sited explanation is plastic bowls. And this is true, but not true. The chemical nature of plastic itself has nothing to do with acne or chin crud. The problem with plastic is it scratches. Those tiny grooves allow bacteria to build up. So for many owners, switching from plastic to ceramic helps.
In my case, my cats already have ceramic plates and stainless steal bowls. With Wendy, the crud is a byproduct of her malformed jaw. While I can help keep it clean (and cleaning her teeth will also help by decreasing the bacteria in her saliva), I will not be able to prevent it.
With James, Tolstoy, and Clancy, it was the food. They got it in period where I was teaching full-time and going to college full-time, so I had little time to make food. I would often mix canned food with my raw food to extend it. Once I removed the canned food, the problem began to resolve itself.