It normally first appears on the chin and in milder cases
appears as small black dots resembling blackheads,
known as comedomes.
Although easily seen on light and short haired cats, these
lesions will be less visible on longhaired breeds. Felines
with greasy fur are often more prone to develop an acne problem.
(Thanks Oliver and Oscar for volunteering for the photos.)
Your cat's sebaceous glands produce an oil (sebum).
It waterproofs your cat's fur, lubricates the skin and is
also used for territorial marking. Although researchers have
not yet determined the exact cause, it has been suggested
that overactive sebaceous glands play a key role in the development
of feline acne.
If too much sebum is produced, hair follicles
can become plugged and the comedomes will appear.
Some of the many other factors that can also play a role:
... dirty chins (cats usually don't clean under their chins
when grooming)
... plastic food dishes
... existing allergies
... an already weakened immune system
... stress or a change in your cat's environment ...
moving
to a new home, a new family member
or maybe a neighborhood bully cat
is roaming around
Cat chin acne can appear as early as six months of age. It
may surface only once, occur occasionally or be a life long
problem for your pet. Hormones are not a factor, as they are
in dogs. Both female and male cats of any breed can develop
acne and the severity of the acne will vary from cat to cat.

The comedomes of the cat acne appear on both the chin and
lip.
They are clustered together giving the chin a dirty
appearance.
Many cases are mild to moderate ... and will
require minimal treatment. My cat Sunnyman had one comedome
breakout and then the acne disappeared. I did stop using plastic
food bowls.
Your veterinarian can often make a diagnosis based on a physical
examination.
There are several other medical conditions that can easily
be confused with feline acne, such as ringworm (which is actually
a fungal infection), yeast infections or food allergies. Your
veterinarian may perform skin scrapings, cultures and biopsies
to rule out the existence of other medical problems.