Otitis externa is one of the most common conditions seen in veterinary practice and one of the most manageable when caught early.
Ear infections, medically termed otitis externa when they affect the outer ear canal, are among the top reasons pet owners bring their animals to the vet each year. While dogs, especially those with floppy ears or allergies, tend to experience them more frequently, cats are not immune. Understanding the causes, recognizing the signs, and knowing how treatment works can make a significant difference in your pet’s comfort and long-term ear health.
Causes
Why Do Ear Infections Develop?
The ear canal of dogs and cats is shaped in an L — a long vertical canal leading to a shorter horizontal segment before reaching the eardrum. This anatomy creates warm, moist environment that can harbor bacteria and yeast if left unchecked. Infections rarely arise from a single cause; instead, they typically involve a combination of predisposing factors, primary triggers, and perpetuating conditions.
Dogs
- Floppy or heavy ear flaps (e.g. Cocker Spaniels, Basset Hounds) that trap humidity
- Environmental and food allergies — by far the most common underlying trigger
- Excessive hair in the ear canal
- Hypothyroidism and other hormonal disorders
- Frequent swimming or bathing without proper drying
- Foreign bodies (grass seeds, debris)
- Ear mites, less often than in cats
Cats
- Ear mites (Otodectes cynotis) — the leading cause, especially in young or outdoor cats
- Allergic skin disease (atopic dermatitis)
- Polyps or tumors in the ear canal
- Immune suppression (e.g. FIV-positive cats)
- Stray or multi-cat household exposure (ear mites are very contagious)
The pathogen picture: Once the ear environment tips toward infection, the usual culprits are bacterial species such as Staphylococcus pseudintermedius and Pseudomonas aeruginosa, or the yeast Malassezia pachydermatis. Many cases involve both simultaneously, which influences which medications are selected for treatment.
Recognizing the Signs
What to Look and Listen For
Symptoms vary depending on whether the infection is bacterial, yeast-based, or mite-related — and whether it is confined to the outer canal or has progressed to the middle ear (otitis media). Common signs include:
- Head shaking or tilting to one side
- Scratching at or pawing the affected ear
- Dark, waxy, or crumbly discharge
- Unpleasant or musty odor from the ear
- Redness, swelling, or heat in the canal
- Pain when the ear is touched
- Apparent hearing loss or balance issues
- Crust or scabs along the ear flap
- Whimpering or behavioral changes
WHEN TO SEEK URGENT CARE: A sudden head tilt, loss of balance, rapid eye movements (nystagmus), or facial drooping indicate the infection may have reached the middle or inner ear — or that a neurological problem such as vestibular syndrome is present. Vestibular syndrome typically occurs independent of external ear canal infections. These neurological symptoms warrant same-day veterinary attention.
Diagnosis
How Vets Confirm the Diagnosis
A proper diagnosis goes beyond identifying that an ear infection is present. The goal is to identify what is causing it and whether the eardrum is intact, since certain medications can damage the inner ear if the drum is ruptured.
Your veterinarian will typically perform an otoscopic exam to visualize the canal and eardrum, followed by cytology — a microscopic examination of a swab sample that identifies the type and relative abundance of bacteria, yeast, and inflammatory cells present. In chronic or recurrent cases, bacterial culture and sensitivity testing helps pinpoint which antibiotics will be effective, particularly when resistant Pseudomonas is suspected.
Treatment
Getting the Ear Healthy Again
Treatment is most effective when it addresses both the active infection and its underlying cause. A course that clears the infection without identifying the root trigger almost always leads to recurrence.
1. Professional ear cleaning
The veterinarian will flush and clean the canal to remove discharge, debris, and biofilm that block topical medications from reaching the infected tissue. For severe or painful cases, this is often done under sedation.
2. Topical antimicrobial medication
The mainstay of treatment is a prescription ear drop combining an antibiotic (e.g. gentamicin, florfenicol) or antifungal (e.g. clotrimazole) with a corticosteroid to reduce inflammation. These are applied once or twice daily for one to three weeks depending on severity. Long-acting single-dose formulations are also available (e.g. Simpler).
3. Ear mite treatment (cats and some dogs)
Mite infestations require a miticide — commonly selamectin, ivermectin, or milbemycin-based preparations. Because mite eggs are not killed by most treatments, a follow-up application two to four weeks later is typically needed. All pets in the household should be treated simultaneously.
4. Systemic medication when needed
Oral antibiotics or antifungals are added when the infection has spread beyond the outer canal, when the eardrum is compromised, or when topical therapy alone is insufficient. Oral corticosteroids (prednisone) may be used short-term to reduce severe swelling that prevents medication from penetrating the canal.
5. Addressing the underlying cause
Managing allergies through dietary trials, allergen immunotherapy, or medications such as oclacitinib or lokivetmab is often the most important long-term step for dogs with recurrent infections. Cats with polyps may require surgical removal.
Follow-up matters: A recheck exam — typically two to three weeks after starting treatment — confirms the infection has cleared and that the eardrum is intact. Stopping medication early based on apparent improvement is a common cause of relapse and antibiotic resistance.
Prevention
Keeping Ears Healthy Long-Term
For many pets, especially allergy-prone dogs, ear infections cannot be entirely prevented but their frequency and severity can be meaningfully reduced with consistent care:
- Clean ears regularly with a veterinarian-recommended ear cleanser, particularly after swimming or bathing. Most ear cleaners have an ingredient that helps the ear dry. Never use cotton swabs, which push debris deeper and can damage the canal. I prefer to use gauze to clean ears.
- Dry the ear canals thoroughly after any water exposure. Fold the ear flap back and allow air circulation for several minutes.
- Keep hair trimmed from around the ear opening for breeds prone to obstruction. Discuss with your vet whether plucking hair from inside the canal is appropriate for your dog. Some breeds such as Poodles and Doodles often have excessive ear hair. I generally do not advocate ear hair plucking unless it is a perpetuating factor.
- Maintain year-round parasite prevention — many broad-spectrum flea and tick preventatives also treat ear mites, which are highly contagious among cats in the same household.
- Address allergies proactively. If your dog has recurring infections despite good hygiene, work with your veterinarian to investigate and manage the underlying allergic disease rather than treating each flare-up in isolation.
- Inspect your pet’s ears weekly as part of a routine grooming check. Healthy ear canals are light pink, odorless, and free of visible discharge or excess wax.
- Schedule routine wellness exams — subtle early-stage infections are far easier and less expensive to treat than chronic, deep-seated ones.
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