External ear infections (otitis externa) are a common problem in dogs and cats. This condition involves the presence of excessive bacteria and/or yeast in the external ear canal. Ear infections can range in severity from mild redness to a severely swollen, painful ear containing large amounts of infected material. Ear infections are often caused by an underlying allergic condition, which may need to be examined in order to prevent recurrent infections. Some dogs with long ear flaps can be prone to yeast ear infections as moisture is trapped in the ear canal. Less commonly ears can be infected with ear mites causing a secondary infection. It is very important to treat all aspects of an ear infection with appropriate medications as determined by your veterinarian. Sometimes external ear infections can spread to the middle and internal ear canals which require advanced diagnostics and treatments. Recheck exams with your veterinarian are invaluable tools to properly monitor treatment of these infections.