Allergic Otitis in Dogs: Why Recurrent Ear Infections Are Often a Sign of Underlying Allergy

A Golden Retriever presents with its fourth ear infection in eight months.

Each episode responds well to topical therapy. The cytology repeatedly shows Malassezia and cocci, yet a few weeks after treatment, the dog is back—head shaking, scratching and uncomfortable.

At this point, changing the ear drops is unlikely to solve the problem.

Instead, clinicians should ask:

"Is this really an ear disease, or is the ear simply the first place where allergy is manifesting?"

Increasing evidence suggests that allergic dermatitis is the most common primary cause of recurrent canine otitis externa, making allergy control just as important as antimicrobial therapy^1,2,3.

The Ear Canal Is Skin—and It Behaves Like Skin

The external ear canal is lined by keratinised stratified squamous epithelium, just like the rest of the skin. Consequently, diseases that affect the skin frequently involve the ears as well^1,3.

In dogs with atopic dermatitis or adverse food reactions, allergic inflammation alters the ear canal by:

• Disrupting the epidermal barrier
• Increasing cerumen production
• Raising local humidity
• Altering the ear microbiome
• Encouraging overgrowth of opportunistic bacteria and yeasts

Secondary infections are therefore often a consequence of allergy rather than the primary disease^1,3.

Why Does Allergy Lead to Recurrent Ear Infections?

Inflammation changes the entire ear canal environment.

Instead of maintaining a healthy, self-cleaning canal, allergic ears develop:

• Excess cerumen accumulation
• Oedema and narrowing of the canal
• Reduced epithelial migration
• Increased humidity
• Microbial dysbiosis

These changes favour overgrowth of organisms such as Malassezia pachydermatis, Staphylococcus pseudintermedius and, in chronic cases, Pseudomonas aeruginosa^1,3.

Repeated inflammatory episodes eventually result in fibrosis, glandular hyperplasia and canal stenosis, making each subsequent infection more difficult to resolve.

Recurrent Otitis May Be the First Sign of Atopic Dermatitis

Not every allergic dog presents with widespread pruritus.

In some patients, recurrent otitis develops before classic skin lesions become obvious^1,3.

Dogs with allergy-associated otitis often have:

• Bilateral ear disease
• Seasonal recurrence initially
• Head shaking and pruritus
• Paw licking
• Facial rubbing
• Axillary or ventral erythema
• Previous improvement with corticosteroids

For this reason, every dog with recurrent otitis deserves a complete dermatological examination—not just an otoscopic examination.

Which Dogs Are Most at Risk?

Large epidemiological studies have shown that breed plays an important role.

Dogs reported to have an increased risk of otitis externa include:

• Cocker Spaniels
• Cockapoos
• Basset Hounds
• Chinese Shar-Peis
• Golden Retrievers
• Labradoodles
• Beagles

Many of these breeds are also predisposed to allergic skin disease, highlighting the close relationship between allergy and recurrent otitis².

Cytology Identifies the Infection—Not the Cause

Ear cytology remains the cornerstone of diagnosis.

It helps determine:

• Whether bacteria or yeast are present
• The predominant organism
• Response to treatment

However, cytology cannot diagnose allergy.

If the same patient repeatedly develops Malassezia or coccal overgrowth, clinicians should investigate the underlying inflammatory disease instead of simply prescribing another topical antimicrobial¹.

Remember:

Cytology explains today's infection—not tomorrow's recurrence.

Allergy Management Is Otitis Prevention

Treating the infection without controlling allergy often results in repeated flare-ups.

Long-term management should include:

• Identification of environmental or food allergens
• Appropriate allergy therapy
• Routine ear examinations
• Maintenance ear cleaning where indicated
• Early treatment of inflammatory flare-ups before secondary infection develops
• Scheduled cytological rechecks

Recent evidence also suggests that proactive anti-inflammatory management in allergic dogs may reduce future otitis episodes by maintaining a healthier ear canal environment³.

Don't Forget the Ear Microbiome

Healthy ears contain diverse bacterial and fungal communities.

During allergic inflammation, microbial diversity decreases while opportunistic organisms become dominant. This imbalance, known as dysbiosis, promotes persistent inflammation and recurrent infections³.

Preserving the normal ear environment through allergy control may therefore be just as important as selecting the correct antimicrobial.

Clinical Pearl

When a dog develops two or more ear infections within a year, don't simply ask:

"Which antibiotic should I prescribe?"

Instead ask:

"What allergic disease is driving these repeated infections?"

Finding and managing that answer is often the key to breaking the recurrence cycle.

Key Takeaways

Allergic dermatitis is the most common primary cause of recurrent canine otitis externa. Secondary bacterial and yeast infections occur because allergic inflammation disrupts the normal ear environment. Ear cytology identifies secondary infections but does not diagnose the underlying allergy. Every recurrent otitis patient should receive a complete dermatological examination. Long-term success depends on treating both the infection and the underlying allergic disease.

References

1. Bajwa J. Canine otitis externa—Treatment and complications. Can Vet J. 2019;60(1):98–101. PMID: 30651659. PMCID: PMC6294027. Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC6294027/
2. O'Neill DG, Volk AV, Soares T, Church DB, Brodbelt DC, Pegram C. Frequency and predisposing factors for canine otitis externa in the UK: a primary veterinary care epidemiological view. Ir Vet J. 2021;74:16. DOI: 10.1186/s40575-021-00106-1. Available from: https://irishvetjournal.biomedcentral.com/articles/10.1186/s40575-021-00106-1
3. Ponn PC, et al. Can We Minimize the Risk of Dogs Developing Canine Otitis Externa? Animals (Basel). 2024. PMCID: PMC11394639. Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC11394639/