How Can You Tell the Difference Between Allergies and Infection?

It’s difficult not to worry if you see your dog's eyes looking irritated. Because eyes are so important, you don’t want to ignore them. Eye problems can come up suddenly. You can go to bed one night, and everything‘s fine. Then the next morning you find that your dog’s eyes are red, watery, goopy, or irritated. That can appear very dramatic, even when the underlying problem is not very serious.

Unfortunately, you can’t often tell the difference between what’s minor and can be treated at home and what’s more serious and needs to be seen by the vet. Also, in either case, irritated eyes can make your dog pretty miserable. The two most common causes of eye problems in dogs are eye allergies and eye infections. It’s important to understand the difference so you can help your dog feel more comfortable and avoid treatment delays.

What are dog eye allergies?

When the immune system overreacts to something in your dog's environment, allergy symptoms can occur. There’s nothing infectious in the eye; instead, it’s inflammation caused by allergies.

Common causes

There are several possible triggers for eye allergies in dogs, including:

• Dust mites

• Pollen from weeds, grass, or trees

• Smoke

• Mold spores

• Cleaning products

• Perfumes, air fresheners, or candles

Some dogs suffer from allergies year-round, while others are seasonal allergy sufferers. Their allergies may be more common in the spring or fall.

Symptoms

If your dog’s eye problems are the result of an allergy, symptoms usually include:

• Red or pink eyes

• Squinting or frequent blinking

• Clear, watery discharge

• Pawing or rubbing at the eyes

• Mild eyelid swelling

• Both eyes are affected simultaneously.

This condition typically causes itchy or irritated eyes rather than painful ones.

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Diagnosis

The diagnosis of allergic conjunctivitis is primarily made by exclusion. You have to rule out more serious problems and, hopefully, find that all you’re left with are possible allergies. The process may include:

• Looking at seasonal patterns or allergy history

• Performing a fluoroscein stain to rule out ulcers

• Examining the eye surface

• Checking for foreign material

There’s no test for eye allergies. Again, it’s mainly a matter of excluding other possibilities.

Treatment options 

There are a few different treatments that may be needed for allergic eye conditions:

• Oral or topical antihistamines

• Steroid or nonsteroidal anti-inflammatory eyedrops

• Artificial tears to flush out allergens 

• Managing underlying skin or environmental allergies

Never put your own eyedrops in your dog’s eyes unless your vet specifically approves.

What is a dog eye infection?

Unlike dog eye allergies, infections usually involve bacteria, viruses, or fungi that actively infect the eye’s tissues. Eye infections typically get worse without prompt treatment.

Types of dog eye infections

Common types include:

• Bacterial conjunctivitis

• Viral infections, which are often secondary

• Fungal infections, which are generally rare and region-specific

• Secondary infections, following trauma, dry eye, or allergies

Unlike eye allergies, infections often start in one eye before spreading to the other.

Symptoms of eye infections in dogs

Signs of infection often include:

• Discharge that can be thick, yellow, green, or white

• Increased redness and swelling

• Crusting around the eyes

• Squinting or holding the eye closed

• Sensitivity to light

• Eye pain

Infections, unlike allergies, are more likely to be painful than itchy.

Diagnosis of eye infections

The diagnostics that your veterinarian needs to use to diagnose an eye infection may include:

• Eye exam and discharge evaluation

• Fluorostein staining

• Bacterial culture if the infection has occurred more than once

• Tear-production testing

• Eyelid and eyelash evaluation

It is essential to get the diagnosis correct so your vet can choose the proper treatment.

Treatment options for eye infections

Treatment may include:

• Antibiotic eyedrops or ointments

• Anti-inflammatory medications

• Antiviral medication when indicated

• Pain management

• Treating underlying conditions

Infections generally improve rather quickly once the proper treatment begins.

Dog eye allergies versus infections

To sum it up, the differences include:

• A clear discharge is usually seen with allergies, while infections cause a thick, discolored discharge.

• Infections are painful, while allergies are itchy.

• Allergies tend to affect both eyes, while infections often start in one.

• Allergies can be recurring or seasonal; infections get worse rapidly.

The safest thing to do to protect your dog’s eyes is assume it’s an infection until proven otherwise.

Related article

Canine Eye Infections: How to Treat Your Dog’s Eye Infection

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When to see a vet

Get in touch with your vet immediately if:

• Discharge is thick, yellow, or green

• Only one eye is affected

• Your dog is squinting or keeping the eye closed

• Symptoms continue for more than 24 to 48 hours

•  The eye appears bluish or cloudy

• Your dog seems to have a painful eye and may be lethargic

Eye problems can get worse quickly and should never be ignored.

How to prevent eye issues in dogs moving forward

Prevention tips that can help you keep your dog’s eyes healthy include:

• Avoid smoke and strong fragrances.

• Gently wipe your dog’s eyes during allergy season.

• Make sure your cleaning products are pet safe.

• Keep bedding clean.

• Keep the hair around the eyes trimmed.

• Be proactive about managing allergies.

• Have your vet examine recurring eye issues early.

Some dogs have long-term allergies and will need long-term management plans instead of just one treatment.

Bottom line

Eye infections and dog eye allergies may look similar, but they’re actually very different problems. Allergies can cause irritation and itchiness, while infections are more likely to cause pain and worsen over time. Clear discharge and the involvement of both eyes indicate allergies; thick discharge and involvement of only one eye often signals infection.

When it comes to eyes, seeing a veterinarian immediately can make all the difference. Guessing is never the right choice; being wrong can cost your dog not only comfort, but also vision.

References

• Aroch, Itamar, et al. “Ocular Manifestations of Systemic Diseases.” Slatter’s Fundamentals of Veterinary Ophthalmology, 2008, pp. 374–418.

• Delgado, Esmeralda, et al. “Diagnostic Approach and Grading Scheme for Canine Allergic Conjunctivitis.” BMC Veterinary Research, vol. 19, no. 1, 3 Feb. 2023.

• Klotz, Stephen A., et al. “Fungal and Parasitic Infections of the Eye.” Clinical Microbiology Reviews, vol. 13, no. 4, 1 Oct. 2000, pp. 662–685.