A swollen canine ear is usually caused by inflammation, which can be accompanied by redness, pain, increased overall body temperature, and some hearing problems. Swelling in a dog’s ear is usually confined to the portion of the ear that is under the ear flap. Because swelling is uncomfortable, a dog with a swollen ear will often shake his head vigorously and scratch at the ear in an attempt to alleviate the discomfort, and may become angry and aggressive. Walking and physical coordination can be negatively affected. 

Ear dermatitis, ear infection and inflammation, and otitis externa are relatively superficial problems that are easy to treat. They do require a veterinary examination and treatment, but should not pose further problems if treated early. Ear hematoma, eardrum rupture, and ear cancer are much more serious problems; each may require surgery.

The origin of a dog’s swollen ear can be traced by location: external, internal, and systemic. External problems, such as ear dermatitis, ear infection and inflammation, otitis externa, and ear hematoma are the most common, while the less common eardrum rupture and ear cancer are more painful, dangerous, and serious, with greater potential for complications.

Ear dermatitis can develop as part of a skin condition that is affecting other parts of your dog’s body, or it can be a reaction to ear mites. Both of these causes create a lot of irritation for your dog, who might exacerbate the situation by scratching the skin until it breaks.  While skin problems can affect any dog, Golden Retrievers, Gordon Setters, and Dachshunds are slightly more likely than other breeds to develop dermatitis of any kind. 

When any foreign body or substance causes an infection in any part of your dog’s ear—outer, inner, or middle—the ear may become inflamed. Canine ear canals are more susceptible to infections than human ear canals, and dogs with exceptionally narrow ear canals or large amounts of earwax are most susceptible to ear infections. These include Shar-Peis, Chow Chows, Bulldogs, Cocker Spaniels, Labrador Retrievers, Springer Spaniels, and Basset Hounds.

Otitis externa is a condition that affects a dog’s outer ear canal, which develops as an irritated response to an accumulation of debris. Bacterial or yeast infections, infections developing from broken skin, flea bites, or ear mites, and tumors can cause otitis externa. Otitis externa may be more likely to develop in dogs with lots of material around their ear areas, such as long floppy ears or lots of thick hair. 

An ear hematoma, a pocket of fluid inside your dog’s earflap, is caused by the bleeding of ruptured vessels. While this can happen to any dog, it’s most likely to develop in dogs with larger, more floppy earflaps. Otitis externa can be a precursor, as the head shaking of an irritated dog can lead the blood vessels in its ear to rupture. 

A dog with an eardrum rupture has a perforated eardrum, which can be caused by exceptionally loud noises, injury, infection in the middle ear, and abrupt changes in atmospheric pressure. It can happen to any dog; no dog has an exception advantage or disadvantage with eardrum ruptures. 

Cancer is an abnormal growth of malignant cells. As is the case with many cancers, there is no certain cause for ear cancer, though an extended period of ear canal inflammation can cause abnormal tissue to develop. Aural inflammation can be caused by ear mites, as well as by bacterial and yeast infections. Infections are more likely to develop in compressed ear canals, which are typical of pug-faced dogs.

Skin conditions are less serious, and require less extensive treatment. If your dog’s swollen ear is due to dermatitis caused by seborrhea, you may be able to treat the problem with mild soap, water, and moisturizer. In every other case, however, your dog will require veterinary treatment for his swollen ear. Dermatitis caused by allergies will require an antihistamine injection, while other causes can require antibiotics or various topical treatments. Ear infections require a thorough cleaning by your veterinarian, followed by medicine to keep the problem from developing any further, possibly including antibiotics. Otitis externa also requires a thorough cleaning, followed by antibacterial medications. 

An ear hematoma usually requires surgery to drain the fluid in the hematoma. Your dog will likely then need pain medication, as well as antibiotics to avoid infection. Otitis externa is sometimes implied in an ear hematoma, so treatment for otitis externa may also be required. An eardrum rupture must also be flushed and carefully cleaned, possibly followed by antifungal medications, antibiotics, and corticosteroids for pain or inflammation. And as with nearly any cancer, your veterinarian will attempt to surgically remove an ear tumor, often followed with radiation or chemotherapy to prevent any recurrence.

As so many cases of swollen ear are caused by improper hygiene or accumulation of debris, ear dermatitis, infections, and otitis externa can be prevented by taking great care to keep your dog’s ears clean inside and out. This can also help to prevent ear hematoma, as the head shaking that creates an ear hematoma is often a response to otitis externa, as well as some cases of eardrum rupture. Keeping your dog away from loud noises can also help to prevent its delicate eardrums from rupturing. And though the causes of cancer are often unknown, if growth of abnormal tissue due to irritation is a cause of some cancers, that too can be prevented by maintaining good hygiene.

The average cost of treating ear dermatitis or ear infection and inflammation is $300, while otitis externa and ear hematoma are a little higher, at an average of $500 each. On the other hand, the average cost of treating ear cancer is about $15,000.