There are two distinct chin problems which seem to be called feline acne:
Black Dust
This is the most common. It is generally accepted
that this is caused by plastic bowls and for many cats the solution is
simply substituting the plastic bowl for a stainless steel bowl or a glass
bowl. When some of my cats had this, changing the bowls did not work.
I stopped giving them milk and the problem was gone. The problem
may be caused by the inability of the cat to clean his chin properly after
drinking the milk resulting in a nutrient rich habitat for bacteria.
Since milk is a great source of water and FLUTD cats need it so much, the
best solution is to clean the cat's chin after it drinks milk.
Acne
Two of my cats also had real acne with swelling of the
chin, purulence (pus) and bleeding (from scratching). I am very conservative
when it comes to medication, specially regarding anti-inflammatories and
antibiotics so I decided to search for alternative treatments before going
conventional. After a long search I found literature that stated
that vitamin E and unsaturated fatty acids, specially linoleic and linolenic
acids, have been used successfully to treat chin acne. I tried it
and it worked. I gave each cat a capsule of vitamin E 400 I.U. two
times per week and one capsule of linoleic + linolenic acid daily and in
two weeks their chins were completely healed. The substances above
present no danger of overdosing or any harmful side effects. They
can be safely used in any circumstance. Premium feeds use vitamin
E as a natural preservative and greater amounts of linoleic and linolenic
acids (the Omegas 3 and 6) when compared to grocery store foods in order
to improve coat quality. They are all essential nutrients and all
commercial feeds have them. How does the deficiency arise then?
Unfortunately, some commercial pet food manufacturers are not aware that
some inorganic ions such as nitrates, nitrites and sulfates destroy part
or all of these oils. This is particularly true for grocery store
brands.