What Causes a Cellulitis Infection in Adult Dogs?

Cellulitis is painful for your dog.
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A dog's cellulitis is not a skin disease but a symptom of a skin problem characterized by areas of firmness, abscesses, redness and painful swelling that's warm to the touch. All cases of cellulitis require prompt veterinary diagnosis and treatment since the condition is highly uncomfortable for dogs.


Pyoderma is most commonly caused by the bacterium Staphylococcus pseudintermedius. In severe cases, the infection reaches deep layers of the skin, and pus may be seen weeping from the skin. Pyoderma can result from a hormonal imbalance, cancer, immune system dysfunction, or a foreign body lodged in the skin. Repeated self-trauma from scratching or biting at skin allergies or fleas also can cause pyoderma. Warm and moist areas of the skin, such as areas a dog's skin folds, have the highest risk for infection because of the potential overcolonization of bacteria.


Demodicosis is one of the most common skin diseases seen by veterinarians. Possible causes of this infection include a weakened immune system, hormones, parasites, poor nutrition and stress. The infection can be localized or generalized. Dogs with demodicosis have increased number of Demodex mites, which live in hair follicles of mammals. A secondary bacterial infection is almost always present with demodicosis, especially due to the increased number of Demodex mites. If the infection is generalized, it's a possible genetic defect that can pass to puppies.


Juvenile cellulitis most commonly occurs between the ages of 3 weeks and 8 months. It's possible, yet rare, for adult dogs to become infected. Juvenile cellulitis is seen on a dog's face, visible parts of the ears and lymph nodes around the mouth. The cause of juvenile cellulitis is unknown, but it's thought to be a dysfunction of the immune system, since most dogs show dramatic improvement when placed on a corticosteroid therapy to suppress the immune system response. Since this form of cellulitis is brought on during the time puppies are vaccinated, vaccines are a possible cause, especially since the immune system is affected.


Even if bacteria is not causing the cellulitis, it can and often does lead to a secondary infection that requires antibiotics. Even if your dog requires lifelong therapy for a skin disease, once treatment begins, the dog often responds favorably to treatments and becomes more comfortable. Since several of these causes results in bacterial infections in combination with a weakened immune system, treatment can be the difference between life or death for the dog.