Allergic Conjunctivitis in Dogs and Cats: When Red Eyes Need a Vet

By Dr Duncan Houston

Red, watery eyes can look like a simple allergy. Unfortunately, a corneal scratch or a painful problem inside the eye can look similar at home.

The safest first decision is whether the eye is comfortable and vision appears normal. Squinting, cloudiness or a sudden change in sight needs prompt examination, even during pollen season.

Quick Answer

Allergic conjunctivitis is inflammation of the tissue around the eye triggered by an allergic response. It can occur in dogs and cats, but infection is an especially important cause of conjunctivitis in cats. Arrange a veterinary eye examination before using medicated drops, and seek urgent care for pain, cloudiness or vision changes.

What does allergic conjunctivitis look like?

The conjunctiva lining the eyelids becomes red and swollen. You may notice watery discharge, rubbing or increased blinking. Both eyes may be affected, and a dog may also have itchy paws, ears or skin.

These clues raise suspicion, but do not confirm allergy. Clear tears do not exclude an ulcer, and thick discharge does not automatically mean a primary bacterial infection. Household sprays and smoke can irritate an eye without causing a true allergy.

Why does the species matter?

In dogs, environmental allergy can be part of a broader skin and eye problem. The vet will still examine eyelids, lashes, tear production and the eye surface.

In cats, infectious causes such as feline herpesvirus and Chlamydia felis need particular consideration. Cornell’s explanation of feline conjunctivitis identifies infection as the major cause and recommends examination when discomfort or discharge occurs. Recurrent signs in a young or multicat household should not simply be labelled hay fever.

How urgent are red eyes?

What must the vet rule out?

Important alternatives include a corneal ulcer, a grass seed or other foreign material, dry eye, inward-rolling eyelids, abnormal eyelashes, glaucoma and inflammation inside the eye. A problem that started in one eye after a walk deserves a careful search for trauma or foreign material.

Examination may include fluorescein staining for ulcers, tear testing and pressure measurement. Cornell’s corneal ulcer guidance explains why surface damage needs prompt attention. Cats with recurrent or severe disease may need tests directed at infectious causes. Allergy testing is not a replacement for this basic eye assessment.

When is this an emergency?

Go urgently for sudden vision loss, a cloudy or enlarged painful eye, severe trauma or chemical exposure. Prevent rubbing if you can safely fit a protective collar. Do not press on the eyeball or remove an embedded object.

If a chemical splashes in, call a veterinary emergency service immediately for flushing instructions and bring the product label. Do not try to neutralise it with another chemical.

How is confirmed allergy treated?

The plan may combine trigger reduction, appropriate lubrication and prescription anti-inflammatory or allergy treatment. The choice depends on species, examination findings and other disease.

Steroid eye drops must not be started before an ulcer has been ruled out. They can worsen important infections and delay ulcer healing. A medicine prescribed for a previous episode or another animal may be unsuitable now. Antibiotics do not treat allergy itself.

What should you do at home?

1. Note which eye started first, possible exposure and any skin itching or sneezing.
2. Gently wipe discharge from surrounding fur with a clean damp pad, without rubbing the eye.
3. Prevent self-trauma and stop fragranced sprays nearby.
4. Use only the eye products your vet recommends and return earlier if pain or vision changes develop.

Common mistakes

• Calling every seasonal red eye an allergy.
• Using human redness-relief drops or leftover steroids.
• Waiting because discharge is clear.
• Starting an elimination diet as a substitute for examining a painful eye.

Reducing repeat irritation

Use low-dust litter, clean bedding and good ventilation. Keep smoke and aerosol cleaners away from animals. For confirmed recurrent allergy, agree on a written flare-up plan that specifies when an examination is required before restarting treatment.

Frequently Asked Questions

Can cats get allergic conjunctivitis?

Yes, but infectious and other eye diseases are important alternatives.

Can I use my own antihistamine eye drops?

Only if your vet approves the exact product for this animal and episode.

Is conjunctivitis contagious?

Allergy is not contagious. Some infectious causes, particularly in cats, can spread between animals.

Should a squinting eye wait until tomorrow?

Seek same-day advice. Marked pain, cloudiness or vision changes need immediate assessment.

Protect the eye before treating the label

Allergy can be manageable once the diagnosis is sound. The first priority is making sure a painful or sight-threatening condition has not been missed.

For help making sense of your animal’s care and preparing questions for your veterinary team, visit ASK A VET™. Urgent symptoms need direct veterinary care.