If a dog's eye is swollen all of a sudden, several health issues could be causing it, including allergies, injuries, infections, or abscesses.

Regardless of the cause, you'll need to head to your veterinarian for treatment. Ignoring it is never the answer because it can be painful for your dog.

Causes of a Dog's Swollen Eye

Depending on the cause, the swelling can occur in one or both eyes. It can happen suddenly or slowly over time. The following causes are some of the most common, but other ailments can cause swelling, too.

Allergic Reaction

One of the most obvious causes of eye swelling in dogs is an allergic reaction. Just like in people, insect bites and stings or exposure to other allergens can cause a dog's eyes to quickly become swollen. Facial swelling along with swelling of the throat can also occur during an allergic reaction, so this acute swelling should not be ignored.

Tumors

Tumors in the mouth, on the face, or in the skull can put pressure on the eyes and cause them to swell (along with nearby tissue). The tumors aren't always obvious. Your veterinarian may not be able to see a tumor without your dog being sedated or fully anesthetized for an X-ray, MRI, or CT scan. They can be painful and their prognosis varies depending on the type of tumor.

Infections

Various types of bacterial infections involving the eye and surrounding tissues can cause inflammation and swelling. Additionally, viral, bacterial, fungal, and even some parasitic infections that affect other parts of the body can cause eye swelling.

Abscesses

Even though they are inside the mouth, tooth root abscesses can cause eyes to swell. The upper fourth premolar is a common culprit for swelling just under the eye because of its long roots. Skin abscess can also cause eye swelling if the abscess is located near the eye.

Glaucoma

Glaucoma is a disease that causes increased pressure inside the eye. The eye can bulge and appear to be swollen or larger than normal.

Dry Eye

Another disease of the eye is keratoconjunctivitis sicca—also known as dry eye. With dry eye, a dog does not produce an adequate amount of tears to keep the eyes lubricated. Consequently, they become dry and inflamed, and they can swell.

Proptosis

Severe trauma can cause an eye to actually pop out of its socket. It's called proptosis, and the eye will appear swollen. Sometimes the eye comes completely out of the socket, though it will often simply bulge.

Injuries

Bite wounds, bumps, and scratches on the face can all cause inflammation and swelling. If these injuries occur near the eye, the eye or the surrounding area may become swollen. Dogfights, being hit by a car, and rough play are common causes of these eye-swelling injuries.

Treatment for Swollen Eyes in Dogs

If one or both of your dog's eyes are swollen, call your veterinarian immediately. They may recommend at-home treatments like warm compresses, a saline eye rinse, or oral antihistamines such as diphenhydramine until you can get your dog into the hospital. Once they examine your dog and determine the cause, they may prescribe eye drops, antibiotics, anti-inflammatories, or steroids. Surgery, dental procedures, and other treatments may also be necessary depending on the cause of the swelling.

How to Prevent Swollen Eyes in Dogs

Because there are so many different causes of swollen eyes in dogs, it can be difficult to prevent. Regular check-ups with your veterinarian can help to detect any problems before they cause the eyes to swell. You should also keep your dog away from stinging and biting insects and situations that may cause trauma to the face.

Basic safety measures will help keep their eyes from being injured and getting swollen. The same goes for regular dental care. Avoid letting your dog chew on things that could crack their teeth, too. This can help prevent tooth-root abscesses from developing.