Hot spots are acute bacterial infections of the epidermis in dogs with Staphylococci (Staph).  Staph are able to produce toxins that kill skin cells, causing rapid and painful ulceration of the skin with patchy hair loss.  Hot spots are also called acute moist superficial pyoderma and pyotraumatic dermatitis.

Bacteria and the Skin

Disease-producing bacteria love warmth, moisture, and darkness.  Healthy skin protects itself from disease-producing bacterial invasion by an intact outer lining (the epidermis) that is constantly reproducing itself and flaking off as a cleaning action.  Skin oils are produced that cover the epidermis and suppress bacterial growth.  The skin surface generally remains dry and if the hair coat is not dense, sunlight will filter through to the surface.  Both dryness and sunlight suppress bacterial growth. 

Hair shafts remain attached to the skin much longer than cells of the epidermis, are not covered by as much oil as the surface of the skin, may be pressed against environment bacterial contaminants, and if the hair coat is thick, provide darkness for bacteria to survive.  Therefore, hair is a common source for bacteria that may invade damaged skin.

Initiating Causes

Summertime provides an excess of reasons to scratch bacteria into the skin lining: fleas, ticks, biting flies, weed seeds in the coat, and allergies are a few examples.  Summer also provides  heat and humidity which enable bacteria to grow faster.  Dogs with thicker hair coats are more susceptible to retaining heat, moisture, and darkness on the surface of the skin.  Once the skin lining barrier is broken, the entry can become infected with bacteria from hair.  As a result, thick-coated dogs in the summertime are the most frequently affected by hot spots.

Signs

The signs of hot spots are a sudden appearance of a round hairless, moist patch of skin.  The dog may frequently lick the spot, or may not, if the pain is too severe.  Surrounding hair may be stuck to the sore.

Diagnosis

The appearance of the skin sore is diagnostic.

Treatment

Treatment does not usually require antibiotics.  The ulceration is superficial and can heal quickly if the skin environment is made less suitable for bacterial growth and reinfection.  CARE IS ADVISED if home treatment is attempted.  The skin sore may be very painful to the dog and there can be a risk of being bit.

* Surrounding hair should be clipped.

* The entire dog should be checked for parasites and then shampooed - rinse thoroughly

* Using a gentle stream of water, irrigate the skin sore until it the serum (slimy material) is rinsed away

* Dilute over-the-counter aluminum sulfate (Domeboro®) as directed on the package and using soaked cotton balls, blot on the sore

* Allow sore to air dry

* Treat for external parasites, if needed

* Blot skin sore with aluminum sulfate solution twice per day if surface is moist

Use of ointments or creams will delay healing if used before the sore remains dry between aluminum sulfate solution treatments.  If marked improvement is not noticed within 24 hours, consult your veterinarian.

Prevention Measures

* Brush out - or clip - dense haired dogs in warm weather

* Keep hair coat clean and dry (between bathes)

* Control external parasites, allergies, and other reasons for excessively scratching the skin

For more information, contact your local veterinarian or the MU Veterinary Medical Teaching Hospital
573-882-7821 or visit  www.vmth.missouri.edu

C.B. Chastain, DVM
Professor, University of Missouri
College of Veterinary Medicine