Feline acne, most commonly found on a cat's chin, is caused by blocked ducts leading to blackheads.  Cats with severe cases may have inflamed pustules or pimples.  The condition can also become so severe that it results in swollen lips and scarring of the chin.  There are many causes for feline acne:  poor grooming, excessive oil production, stress and food allergies, and plastic food and water dishes that serve as a breeding ground for bacteria. 

Other conditions that may mimic feline acne, such as ringworm, food allergies, yeast infections, and mange mites, should be ruled out by your vet.  Once all other conditions are ruled out, you should treat your cat to prevent secondary infection.  Most vets will recommend daily cleaning of the infected area with an antibiotic soap followed by topical ointment.  Oral antibiotics may be prescribed as well as antibacterial surgical scrub.