👂 Why Do the Ear Infections Keep Coming Back?

The Four Layers (PSPP)

Veterinary dermatology classifies otitis externa into four categories, usually abbreviated PSPP. Understanding which layer the treatment is addressing explains almost everything about why some ears clear and stay clear while others become a permanent feature of your life.

Ear drops treat the secondary layer. That is genuinely useful — the infection is real and needs clearing — but if the primary cause is untouched, the canal becomes inflamed again and the organisms come back with it. That single mismatch is the mechanism behind most recurring ears.

Allergy Is the Usual Primary Cause

In dogs, the numbers are lopsided. Veterinary literature puts atopic dermatitis as the primary cause in roughly 43% to 75% of canine otitis externa, and a retrospective series of 100 dogs found allergic dermatitis the most common primary cause, followed by grass awns.

The detail that surprises most owners: up to 24% of dogs with an adverse food reaction have otitis externa as their only complaint. No itchy skin, no paw licking, no rash — just ears. So "it can't be allergies, his skin is fine" is not the reassurance it sounds like.

The distinction between food and environmental allergy matters for what you do next, and seasonality is the most useful clue an owner has. Environmental allergy classically flares with pollen seasons; food reaction runs year-round. If a diet trial is on the table, our Elimination Diet Trial Planner lays out the schedule and the contamination audit that decides whether it actually proves anything.

When One Ear Changes the Answer

Allergy affects the whole animal, so allergic otitis is typically bilateral. Veterinary guidance is that a consistently one-sided case should raise the priority of other explanations: a foreign body such as a grass awn, a polyp, a growth, or middle ear disease. This is a discriminator owners can actually apply at home. A dog that suddenly starts violently shaking its head and pawing at one ear after a walk through long grass has a plausible grass seed in there, and that is a same-day appointment — awns migrate and do progressive damage.

Why Cytology Every Time, Not Just the First Time

A swab examined under the microscope is described in veterinary practice as the most valuable diagnostic tool in otitis, because it identifies what is actually growing and the treatment differs by organism. You cannot distinguish yeast from rod-shaped bacteria by smell or appearance, and a recurring ear frequently changes organism between episodes — so drops that worked in March may be the wrong drops in September. Rods in particular tend to signal a more difficult infection. If you have been handed medication without a swab, asking for cytology is a reasonable and cheap request.

Cats Are a Different Picture

Allergic otitis is less common in cats than in dogs, which shifts the likely primary causes. Ear mites are a leading cause in kittens and young cats and are contagious between pets in the household. In an adult cat, particularly with a stubbornly one-sided problem, inflammatory polyps and growths climb the list — and those need a vet to look rather than another course of drops. Dark, crumbly, coffee-ground debris is classic for mites but is not diagnostic on its own, which is another reason the swab matters.

The Damage That Does Not Reverse

Chronic inflammation thickens the canal lining, narrows the lumen and can eventually mineralise it, and veterinary sources note these changes can become irreversible where otitis has been inadequately treated. Once the canal has closed down, medication struggles to reach the tissue and surgery may be the remaining option. Middle ear involvement is common in long-running cases — reported in over half of chronic or recurrent cases in one summary — and an infected middle ear reseeds the outer ear indefinitely. This is the honest argument for pushing on the underlying cause early rather than settling into a rhythm of managing flare-ups.

Frequently Asked Questions

Why does my dog keep getting ear infections?

Because the infection is usually the consequence, not the cause. Veterinary dermatology uses a four-part framework — primary causes, secondary infection, predisposing factors and perpetuating factors — and the ear drops only address the secondary layer. Allergic skin disease is the primary cause in a large share of cases; figures in the veterinary literature put atopic dermatitis behind roughly 43% to 75% of canine otitis externa. Clear the yeast and bacteria without touching the reason the canal keeps becoming inflamed and the canal simply becomes inflamed again.

Can food allergies cause ear infections in dogs?

Yes, and sometimes ears are the only sign. Work cited in veterinary otology reports that up to 24% of dogs with an adverse food reaction present with otitis externa as their sole clinical complaint — no itchy skin, no paw licking, just ears that keep flaring. That is worth knowing because it inverts the usual assumption that a food allergy would show up on the skin first. If your dog's ears keep recurring and nothing else seems wrong, a diet trial is a reasonable conversation to have with your vet.

Why is only one ear infected?

That asymmetry is a useful clue. Allergic otitis is usually bilateral because the allergy affects the whole animal, so veterinary guidance is that a one-sided case should raise the priority of other explanations — a foreign body such as a grass awn, a polyp, a growth, or middle ear disease. A dog that suddenly starts shaking its head and pawing at one ear after being in long grass is a same-day appointment rather than a wait-and-see, because a grass seed migrating down a canal does real damage.

Can I treat my dog's ear infection at home?

Not safely, and the reason is specific rather than precautionary. If the eardrum is perforated, some ear medications and cleaners can reach the middle ear and cause damage including hearing loss — which is why veterinary sources treat otoscopic examination as mandatory before treatment, since a perforated eardrum fundamentally changes what can be used. You cannot see the eardrum from outside. Leftover drops from a previous infection are a particularly common mistake, because the organism this time may be different from last time.

What is cytology and why does it matter every time?

Cytology is a swab of the ear examined under a microscope to identify what is actually growing — yeast, cocci, rods, or a mix. It is described in veterinary practice as the most valuable single diagnostic tool in otitis, because the treatment differs by organism and you cannot tell them apart by how the ear looks or smells. It matters at each episode rather than just the first, because a recurring ear frequently changes organism between flare-ups, and rod-shaped bacteria in particular tend to signal a harder problem.

Can chronic ear infections cause permanent damage?

They can. Repeated inflammation thickens the canal lining, narrows the canal and can eventually mineralise it, and veterinary sources note these changes can become irreversible when otitis is inadequately treated. At that point medication struggles to reach the affected tissue and surgery may become the remaining option. Middle ear involvement is also common in long-running cases — reported in over half of chronic or recurrent cases in one summary — and an infected middle ear acts as a reservoir that reseeds the outer ear. This is the argument for treating recurrence seriously early rather than managing flare-ups indefinitely.