Otitis externa is characterized by itchy ears, redness, local swelling, and if infected, a discharge with very bad odor. The nature of the odor and discharge depends on what the causative agent is.
The term otitis externa does not imply a cause; simply that the canal is inflamed. As mentioned above, foreign bodies such as grass awns, moisture (as from swimming in a lake), bacteria, yeast, and ear mites are all potential causes of inflammation and resulting infection or infestation.
If known, one would list the cause of the otitis before the term, such as: bacterial otitis externa or fungal otitis externa to be more specific.
Treatment of otitis externa depends on the cause. A good ear cleansing is helpful for most cases of otitis externa. Antibiotics in the ear (and possibly by mouth as well) will help with bacterial problems and foreign body penetration. Antifungal and antiparasitic solutions will help with yeast and mites.
If your pet has a bad odor from the ears, is scratching or shaking the head constantly, please see your veterinarian as soon as possible to prevent further damage to the ears and ear drums.All About Ear Infections