Diagnosis: Otitis Externa

The cause of this infection could be a rampant overgrowth of yeast in the ear canals. Here are the signs you should look for.

Among all acquired feline ear disorders, the most common by far is otitis externa, an infection of the outer ear canal that, if untreated, can progress to the inner ear, damage the ear drum, and seriously compromise an animals hearing as well as its sense of balance. The most common cause of this unpleasant condition and its potentially deafening consequences is an assault on the ear by an outside invader, the ear mite. In some cases, however, the culprit is an organism that normally resides harmlessly within a cats ear – a one-celled fungus, or yeast, known as Malessezia.

Causes of Ear Infections

Bev Caldwell


“All feline ears have Malassezia in them,” explains William Miller, VMD, a board-certified member of the American College of Veterinary Dermatology and medical director at Cornell Universitys College of Veterinary Medicine. “Its just part of the natural flora. But if something changes the climate in the ear, the organisms begin to multiply and become too numerous – and you end up with infection.”

Contributing Factors

Several factors can precipitate the hazardous proliferation of Malessezia, which tends to occur in a warm, damp environment, Dr. Miller points out. An allergic disease of some sort, for example, can make the surface of the ear canal abnormally moist and thus foster yeast growth. The excessive accumulation of wax in the canal may also be responsible, since yeast organisms feed on that gooey substance. A cat that likes to go swimming would be at greater risk, of course, but this would be an extremely rare cause of yeast growth, since, as Dr. Miller dryly observes, “Most cats, unlike dogs, fail to take pleasure in swimming.”

Among all causes, he observes, the most typical is the prolonged and inappropriately routine use of liquid ear cleaners by overzealous owners who are unaware that the constant lubrication of an animals ear canals is bound to be counterproductive. Says Dr. Miller, “Some owners just cant keep themselves from futzing around with their cats ears.” All cats are susceptible to Malessezia proliferation in their ears, he notes, although animals living in warm, humid climates are at greater risk.

Clear Indications

The signs of what Dr. Miller refers to as “yeast otitis” are the same as those associated with otitis externa in general: The cats outer ear is likely to be inflamed, and the animal will hold its ears flat back against its head, scratch at them without letup, and shake its head frequently – as if trying to dislodge a bothersome object. The cat may walk unsteadily, behave in an uncharacteristically lethargic manner, and respond as if in pain if its ears are touched.

Otitis externa caused by various other infections can potentially spread to the middle ear, eardrum and inner ear and cause deafness. However, Malessezia is eminently treatable, Dr. Miller says, noting that he has never seen a yeast infection that progressed beyond the outer ear, even though the natural flora in a cats ears normally thrive as far as the ear drum and even beyond. “The yeast can cause irritation in the ear canal,” he says, “and there can be a lot of debris and goo in there that can affect a cats ability to hear. But a yeast infection will rarely cause permanent deafness.”

Diagnosis will usually entail a review of an animals medical history and a thorough physical examination, with special attention given to the affected ear or ears. For this, the veterinarian is likely to use an otoscope – a flashlight-like instrument that provides a magnified view of the ears inner depths. Also, says Dr. Miller, “Well clean out the ear and use a microscope to examine a sample of the debris in the ear canal – and with Malessezia infection, there will be lots of it. If we determine that a yeast overgrowth and nothing more is the problem, well institute antiyeast therapy – eardrops or pills. The clinical signs will usually disappear entirely within two to four weeks. If they dont, well try to find out what other ear condition is causing the problem.”

Dr. Miller strongly cautions owners against trying to relieve a cats ear problems on their own. If the signs of a hearing disorder in an animal become apparent, always seek veterinary consultation, he advises.