Have you noticed that your dog's eyes appear bloodshot? Your dog's eyes could be red for a number of reasons. Here are some of the most common causes:

Irritation
If a foreign object, such as dirt, dust, grass or hair gets in your dog's eye, it can cause irritation and redness. Cleaning sprays and perfume can also irritate your dog's eyes.

Signs of irritation:

Redness
Tears or watery discharge
Itchy eyes (expressed by pawing at their eyes or rubbing their face)
Treatment: You should contact your veterinarian first before any applying any treatment. They may suggest to gently wash out your dog's eyes with lukewarm water. Wait an hour or two to see whether the redness clears up.

Allergies
Just like people, dogs can have allergies, too. They can have seasonal allergies and food allergies, as well as allergic reactions to dust, mold, household cleaners and other environmental allergens. Any of these allergies can cause a dog's eyes to turn bloodshot, says the American Kennel Club.

Signs of Allergies:

Redness
Tears or watery discharge
Itchiness
Licking and scratching
Sneezing
Red or inflamed skin
Hair loss
Treatment: Don't give your dog over-the-counter allergy medicine or eye drops without first consulting your veterinarian. Proper treatment depends on your dog's specific allergy, which your vet will determine by examining your dog and running tests. In some cases, pinpointing allergens can be a long process, especially if your vet suspects a food allergy (12-week food trials are required to properly diagnose food allergies).

Pink Eye
Pink eye, the common name for conjunctivitis, comes in two forms: infectious and non-infectious. Infectious pink eye is caused by a virus or bacterial infection, while the non-infectious type is generally caused by allergies, irritation, injury, a congenital condition or an illness such as distemper.
Signs of Pink Eye:
Red or puffy eyes
Itchy eyes
Eye discharge
Eyelids sticking together, squinting
Swelling of the eyelid lining (conjunctiva)
Treatment: Whether or not your dog's case of pink eye is infectious, it needs to be checked out and treated by a vet. They'll determine whether it's the contagious type before determining and treating an underlying cause. Infectious pink eye must be treated with antibacterial or antifungal medicine. Your vet may also give you anti-inflammatory medicine to administer to your dog.

Dry Eye
Another issue that might cause you to wonder why your dog's eyes are red is dry eye, the common term for keratoconjunctivitis sicca (KCS). This condition occurs when the tear glands don't produce enough moisture, causing the tissues of the eye to dry out, says Cuteness. Dry eye can be a result of eye trauma, an underlying health condition or a corneal ulcer.

Signs of Dry Eye:
Redness
Itchy, painful eyes
Thick discharge
Treatment: Your vet will conduct a test to assess the level of moisture your dog's tear glands are producing. They may also check for corneal ulcers. Dogs with dry eye are commonly prescribed eye drops to keep their eyes moist. You'll need to clean their eyes on a regular basis. While dry eye sometimes clears up on its own, it can also be chronic and require lifelong treatment.

Glaucoma
Glaucoma is a painful condition caused by fluid buildup that creates swelling and pressure, leading to damage of the optic nerve. If left untreated, glaucoma can lead to blindness.

Signs of Glaucoma:

Redness
Pain
Swollen eyes
Receding eyeballs
Cloudy appearance
Dilated and unresponsive pupils
Poor vision
Treatment: If your dog shows signs of glaucoma, bring them to the vet immediately. If you manage to catch the condition early enough, there's a better chance that topical medicine or laser surgery will be effective and that your dog's vision can be saved, says Cuteness. In more severe cases, surgery may be required to relieve pain caused by fluid buildup and pressure. In the most severe cases, surgical removal of one or both eyes may be required.

Side portrait of a shepherd mix with eye closed sitting outdoors.

In addition to the causes listed above, red eyes in dogs can be a sign of an illness, such as distemper, or a chronic health condition like diabetes or hyperthyroidism. Red eyes can also indicate a tumor or certain types of cancer. Some dog breeds are more prone to eye problems than others. This includes flat-faced breeds like pugs and bulldogs, as well as long-haired breeds whose hair can irritate or damage their eyes. Dogs also become more prone to eye problems and underlying health conditions that can cause eye redness as they age.