1. General Considerations

   1. Canine acne is most likely a primary inflammatory reaction of hair follicles of the chin, around the lips and muzzle areas and not a keratinization disorder.
   2. It is a common disorder of short-coated breeds and develops at a young age.
   3. The specific cause is unknown. The increased incidence in short-coated breeds could be related to the structure of hair follicles that grow short hair coats, which make them more prone to trauma. Examples of overrepresented breeds include English bulldogs, boxers, Doberman pinschers, weimaraner, mastiffs, rottweilers, Great Danes and German shorthaired pointers.
   4. Secondary bacterial folliculitis is common and involved organisms include Staphylococcus pseudintermedius and in rare cases Staphylococcus aureus.

2. History and Clinical Signs

   1. The history usually includes the presence of lesions on the chin, around the lips, and muzzle starting at a young age in short-coated dog breeds.
   2. In mild cases, spontaneous remission may occur.
   3. Clinical signs are variable.
   4. Lesions may be limited to the anterior aspect of the ventral chin or may extend to areas around the lips and muzzle.
   5. Initial lesions include erythematous papules and nodules.
      1. If secondary bacterial infection develops, pustules and yellowish crusts will form in one more of these sites.
      2. In severe cases, the affected hair follicles rupture resulting in worsening of the inflammatory process and eventually the formation of draining tracts and/or deep erosions to ulcerations.

3. Diagnosis

   1. A tentative clinical diagnosis is made based on the history, age of onset, breed, and clinical appearance of lesions.
   2. Differential diagnoses include demodicosis and bacterial folliculitis/furunculosis.
      1. Therefore, skin scrapings and cutaneous cytology (i.e. direct smears of exudate) should be routinely performed.
   3. Bacterial culture and susceptibility testing is recommended in cases with deep lesions (i.e. draining tracts) if systemic antibiotic is considered.
      1. The authors recommend practicing antibiotic stewardship and treating the secondary infection topically before considering systemic therapy.
   4. Skin biopsy is rarely needed and should be considered in cases with unusual presentation.

4. Treatment

   1. Treatment depends on the severity and chronicity of the problem.
   2. Mild cases of chin acne need no treatment and may spontaneously resolve.
   3. If active lesions such as papules and pustules are present but the case is mild, topical treatment with products containing benzoyl peroxide such as shampoos (e.g. Pyoben®, OxyDex®, SufOxyDex®) and gels(e.g. OxyDex gel®, Pyoben gel®) can be tried first.
      1. Benzoyl peroxide is effective because of its keratolytic effect (i.e. comedonelytic or follicular flushing) and antimicrobial activity.
      2. Be mindful that benzoyl peroxide based gels and ointments can be irritant to the skin.
      3. This therapy is used twice daily until the condition is controlled and then as needed for maintenance therapy.
   4. If a secondary bacterial infection is present and cocci-shaped bacteria are seen on cytology, mupirocin ointment (Bactoderm®, Muricin®) can be tried.
      1. Mupirocin has excellent activity against gram-positive cocci, is bactericidal, works well in acid pH, and is not systemically absorbed.
      2. Apply mupirocin initially every 12 hours and then as needed.
      3. However, this antibiotic should be used only in severe chronic cases or cases associated with resistant bacterial infections because it is an important antibiotic used in methicillin-resistant Staphylococcus aureus (MRSA) infections in humans.
   5. Topical glucocorticoids such as betamethasone valerate ointment may be beneficial to reduce inflammation and pruritus.
      1. If bacterial infection is present, ointments containing a glucocorticoid and antibiotic should be used.
      2. Products containing antibiotic should be used twice daily until the secondary infection is resolved (~2-3 weeks). Perform skin cytology and bacterial culture to determine if the infection is completely resolved.
      3. Products containing solely glucocorticoids can be used daily for 2-3 weeks and then 1 to 3 times weekly as needed to maintain the disease controlled. More frequent use can cause skin atrophy or more severe side effects.
   6. Systemic antibiotics should be prescribed until complete resolution of clinical signs and a negative skin cytology and bacterial culture.
      1. Pinch the skin at previously affected areas to make sure the deep infection is resolved (i.e. no drainage is established) as the skin surface can heal before the deep tissue.
   7. If marked edema and deep inflammation are present, prednisone/solone (about 1 mg/kg orally per day) may be given for no longer than 7 to 14 days.
   8. In the few cases that are refractory to routine topical therapy, the synthetic retinoid, tretinoin (Retin-A®) can be used topically q 12h. However, there is only anecdotal reports of its efficacy in canine acne.
      1. This drug can irritate the skin.
      2. Sunlight has to be avoided during therapy.

References

Kwochka KW: Primary Keratinization Disorders of Dogs.  In: Griffin CE, Kwochka KW, MacDonald JM (eds).  Current Veterinary Dermatology.  St Louis, Mosby Year Book, 1993; p 176-190.

Kwochka KW: Overview of normal keratinization and cutaneous scaling disorders of dogs.  In: Griffin CE, Kwochka KW, MacDonald JM (eds).  Current Veterinary Dermatology.  St Louis, Mosby Year Book, 1993; p 167-175.

Miller, Griffin and Campbell.  Chapter 14. Keratinization defects. In: Muller & Kirk’s Small Animal Dermatology. 7th ed., W.B. Saunders, Missouri, 2013; p 630-646.

Power HT, Ihrke PJ.  Synthetic retinoids in veterinary dermatology.  Vet Clin North Am: Small Anim Pract, Philadelphia, WB Saunders, 1990; p 1525.