Disease Spotlight: Ear Infections 

According to one popular pet insurance company, ear infections are the number one reason dogs, and number eight reason cats, visit their veterinarian. The ear canal is lined with a thin layer of skin that contains glands and hair follicles all confined in a small space that is warm and dark. The skin naturally harbors low numbers of Staphylococcal bacteria and Malassezia yeast. Adding in predisposing, primary, secondary and perpetuating factors makes a recipe for ear infection.

Factors that Lead to Infection

  • The most common predisposing factors are excessive hair in the canal (poodle parents know what this means), genetically narrow or waxy canals (cocker spaniels), and excessive moisture from swimming (water-loving Labrador friends). Pets can also have polyps or tumors in their ear canals.
  • The primary factors are allergies (food and environmental), disorders that slow down epithelial turnover, foreign bodies and parasites.
  • Secondary factors come into play when the bacteria or yeast overgrow or when cleaning agents are used too often and ears are being over cleaned.
  • Finally, with chronic and repeated infections the perpetuating factors—such as swelling of the skin inside the canal, hardening of the normally soft cartilage and infection that breaches into the middle ear—make resolution of the otitis even more difficult.


Ear infections usually involve some combination of redness, itch, discharge, odor, pain and hearing loss. The age at which the infections first start and how often they recur help your veterinarian look for an underlying cause. For example, a food allergy can often manifest as ear infections. They are typically difficult to resolve and recur very quickly.

Interestingly, we see many patients with environmental allergies that experience relapsing ear infections. Initially, these patients tend to show a relative ease in ability to clear the infection and tend to be able to go a period of time before the infection recurs. However, here in Texas, infections tend to progressively get worse each year.

Testing and Diagnosis

Ear infections can be caused by numerous different bacteria and one primary species of yeast. For this reason, cytology is a critical test to determine which microorganism(s) is/are the causative agent. To choose appropriate therapy, your veterinarian will swab the ear, stain the sample and look under a microscope. Therapy will depend on the type, severity and depth of the infection. Cleansers, true medications and steroids are commonly needed.

Some ear infections breech into the middle ear canal. Your veterinarian will need to address that deep infection appropriately, otherwise the infection will continue to recur.

Addressing the underlying allergy is also critical. Dermatologists at the ADRC specialize in investigating and addressing not only the infection, but also the underlying cause.

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