Rethinking Otitis Externa: A Practical Approach to Ear Disease in Dogs and Cats

Otitis externa remains one of the most frequently encountered conditions in small animal practice, accounting for approximately 10–20% of canine consultations and representing a significant proportion of dermatology appointments. Although considerably less common in cats, chronic otitis can still be clinically challenging, particularly in patients with allergic skin disease, ectoparasites or conformational abnormalities.

Despite advances in veterinary dermatology, recurrent otitis continues to frustrate both clinicians and owners. In many cases, the problem is not a lack of effective therapeutics but rather delayed diagnosis, inappropriate empirical antimicrobial use and insufficient attention to maintaining a healthy ear canal environment.

Successful management requires more than simply treating infection—it requires understanding how changes in the ear canal microenvironment drive microbial overgrowth and recurrence.

Otitis is a Year-Round Disease

Although many practitioners associate otitis with the summer months, seasonal patterns are often more complex and largely reflect changes in environmental allergens, humidity and animal behaviour.

During spring, increasing pollen counts commonly trigger allergic flare-ups in predisposed dogs. Inflammation associated with atopic dermatitis frequently affects the ears before other areas of the body, altering cerumen production and creating favourable conditions for secondary microbial overgrowth.

In summer, higher temperatures and increased humidity encourage proliferation of both bacteria and Malassezia pachydermatis. Swimming, bathing and outdoor activities further increase moisture within the external ear canal, particularly in breeds with pendulous pinnae or narrow ear canals. Persistent moisture alters the normal microenvironment, reduces ventilation and promotes microbial multiplication.

Autumn often brings another rise in otitis cases as environmental mould spores increase and allergic patients experience secondary seasonal flare-ups. Dogs returning from holidays may also present following repeated exposure to swimming or prolonged outdoor activity during warmer months.

During winter, while environmental humidity decreases, indoor heating can alter skin barrier function and exacerbate chronic allergic disease. Dogs spending more time indoors may also experience increased exposure to house dust mites, another important trigger for atopic dermatitis. Patients with chronic otitis frequently relapse during this period if underlying dermatological disease remains poorly controlled.

Rather than being considered a seasonal disease, otitis externa should therefore be viewed as a condition influenced by multiple environmental factors throughout the year, requiring preventive management tailored to individual patient risk.

Cytology Should Guide Therapy, Not Follow It

One of the greatest opportunities to improve otitis management lies in reducing empirical antimicrobial use.

Although topical antibiotics remain invaluable when genuinely indicated, their routine use without cytological confirmation contributes to unnecessary antimicrobial exposure and increases selection pressure for resistant organisms.

Ear cytology is rapid, inexpensive and provides immediate clinical information that directly influences treatment decisions.

A well-prepared smear allows differentiation between:

• Malassezia overgrowth

• Gram-positive cocci

• Gram-negative rods

• Mixed infections

• Inflammatory cell populations

  
  

This distinction is clinically important because not all otitis cases require antibiotics.

Many cases involve predominantly yeast overgrowth or inflammatory disease, where management should focus on correcting the underlying ear environment rather than immediately prescribing antimicrobial therapy.

When rod bacteria predominate—particularly if Pseudomonas aeruginosa is suspected—culture and antimicrobial susceptibility testing should be strongly considered before selecting treatment.

Incorporating routine cytology into every otitis work-up not only improves therapeutic success but also supports responsible antimicrobial stewardship.

Restoring the Ear Canal Environment

The external ear canal possesses a delicate balance of temperature, humidity, pH and lipid composition that normally limits microbial proliferation.

Once this balance is disrupted, opportunistic organisms rapidly multiply, perpetuating inflammation even after the initiating cause has resolved.

For this reason, modern ear cleaners should be viewed as therapeutic tools rather than simple wax removers.

The Importance of Drying Agents

Excessive moisture is one of the most important factors promoting microbial overgrowth, particularly in swimming dogs and patients with recurrent otitis.

Boric acid has long been recognised as an effective drying agent because it helps reduce moisture while gently acidifying the ear canal. Lowering canal pH creates an environment that is considerably less favourable for both bacterial and yeast proliferation.

Unlike alcohol-based drying formulations, boric acid achieves this effect without excessive irritation, making it well suited for routine maintenance in predisposed patients.

Glycolic Acid: An Alternative to Acetic Acid

Organic acids are widely used in veterinary ear cleaners because of their ability to acidify the ear canal and inhibit microbial growth.

Acetic acid has traditionally fulfilled this role and demonstrates excellent antimicrobial activity. However, its relatively low pH frequently produces a stinging sensation when applied to inflamed ears, reducing owner compliance and making repeated application uncomfortable for patients.

Glycolic acid provides an alternative approach that minimises the likelihood of a stinging sensation.

As the smallest alpha-hydroxy acid, glycolic acid effectively lowers ear canal pH while exhibiting keratolytic properties that help loosen cellular debris and excessive cerumen. Importantly, it is generally better tolerated than acetic acid on inflamed tissues, allowing clinicians to achieve canal acidification with improved patient comfort and owner acceptance.

For long-term management, particularly in patients requiring frequent ear cleaning, improved tolerability can be as important as antimicrobial efficacy.

Supporting the Skin Barrier

Chronic otitis is accompanied by disruption of the epithelial barrier lining the external ear canal.

Repeated inflammation damages intercellular lipids, increases transepidermal water loss and compromises normal epithelial repair, creating conditions that favour recurrent microbial colonisation.

Ceramides play a central role in restoring barrier integrity. By replenishing essential epidermal lipids, they help improve epithelial cohesion, reduce water loss and support recovery of the normal skin barrier.

A healthier epithelial surface is less susceptible to chronic inflammation and may reduce the persistence of microorganisms by restoring normal defence mechanisms.

Maintaining barrier function should therefore be considered an integral component of long-term otitis management rather than an afterthought once infection has resolved.

Matching Ear Cleaners to the Clinical Presentation

Not all ear cleaners serve the same purpose, and selecting an appropriate formulation depends on cytological findings and the suspected microbial population.

When cytology demonstrates significant Malassezia overgrowth or patients are predisposed to recurrent yeast otitis, formulations combining boric acid with glycolic acid provide several complementary benefits. They help maintain an acidic, relatively dry ear canal while supporting removal of debris and creating conditions that discourage further yeast proliferation.

This is the rationale behind formulations such as Abelia GlycoZoo®, which combine these mechanisms into a maintenance ear cleaner suitable for patients prone to recurrent ceruminous otitis. Rather than functioning as an antimicrobial drug, its role is to optimise the ear canal environment and reduce the conditions that favour recurrence.

Where bacterial otitis is present—particularly infections involving Gram-negative organisms—a different strategy is often required.

Tris-EDTA increases bacterial membrane permeability by chelating divalent cations that stabilise the outer membrane of Gram-negative bacteria. This weakens the bacterial cell envelope, enhances penetration of topical antimicrobials and has also demonstrated activity against bacterial biofilms, an important contributor to chronic and recurrent otitis.

The addition of benzyl alcohol provides complementary antiseptic activity, particularly against Gram-positive organisms, while also contributing mild local anaesthetic properties that may improve patient comfort during application.

Formulations such as Abelia TrisEDTA®, combining Tris-EDTA with benzyl alcohol, therefore provide an evidence-based approach to preparing the ear canal in bacterial otitis and may improve treatment success, particularly when used alongside appropriately selected topical antimicrobials guided by cytology and, where indicated, culture.

Looking Beyond Infection

Otitis externa should no longer be viewed simply as an infection requiring antibiotics.

Instead, it represents a multifactorial disease in which inflammation, disruption of the ear canal microenvironment and impaired epithelial barrier function create ideal conditions for microbial overgrowth.

Routine cytology, appropriate selection of ear cleansers and maintenance of a healthy ear canal environment are fundamental components of successful long-term management. By matching ear cleaning protocols to the predominant microbial population and underlying pathology, clinicians can reduce recurrence, improve patient comfort and support responsible antimicrobial stewardship while achieving better clinical outcomes.