Ask a Vet: Why Do Dogs Get Eye Boogers? What About Tear Stains?

My pal Buster’s eye boogers don’t bother him, but they certainly annoy me. My dog is a very cooperative fellow, so he doesn’t resist or struggle as I remove the nastiness from the hair next to his eyes. When it comes to eye boogers, the only thing I dislike more than removing them is leaving them in place. Eye boogers are gross.

Over the years, clients have brought up the related subjects of eye boogers and tear stains many more times than I can count. What are eye boogers and why do dogs get them? Are they more than just an unsavory nuisance? And why on earth are tear stains red?

Dr. Eric Barchas. (Photo by Liz Acosta)

“Why do dogs get eye boogers?” may be the easiest question to answer, if a tongue-in-cheek answer is acceptable. Dogs get eye boogers because they don’t have fingers.

But seriously, the accumulations of mucus and fat known as eye boogers are nothing more than dried-up tears.

If you thought tears were watery, you were only partly correct. Although tears may seem like a simple saline solution, in fact they are much more complex. Very few things about bodies are as simple as they seem.

Tears have three major components. There is the watery component with which everyone is familiar. In addition, tears contain mucus and fat. Together, these components keep the eye moist and lubricated. They also provide oxygen and nutrients to the cells of the cornea, which under normal circumstances has no blood vessels to supply it.

Water evaporates. Fat and mucus do not. Eye boogers are made of the fat and mucus left over when the watery component of tears has evaporated. They can become quite large in dogs because, as I already pointed out, dogs don’t have fingers with which to remove them.

Although eye boogers are normal in dogs, people should be aware that excessive eye boogers may be a sign of trouble. There are many conditions, ranging from eye infections to foreign bodies to ulcers to insufficient tear production, that may cause extra mucus to build up in and around an eye. (Paradoxically, dogs who don’t produce enough of the watery component of tears are predisposed to excessive eye boogers.)

How can you tell whether your dog’s eye boogers are normal, or whether they’re excessive and the result of an eye problem? The only way to be certain is to visit the vet, who may test for adequate tear production, glaucoma, and ulcers on the cornea. However, eye boogers rarely are the only symptom of eye problems. Most dogs with eye problems will have other signs such as squinting, itching, or redness of the eye.

Under normal circumstances, glands around the eye produce tears. The tears coat the eye, and then drain into the nose through a duct (called the nasolacrimal duct) that starts on the lower eyelid. Eye boogers develop when the watery portion of the tears evaporates. Tear stains occur when tears are produced more rapidly than they drain.

I already mentioned that tears contain water, fat, and mucus. But it doesn’t end there. They also contain proteins. And they contain porphyrins.

Porphyrins are components of one of the body’s most famous molecules — hemoglobin. Hemoglobin is what makes blood red. Porphyrins generally are brightly colored molecules, and the porphyrins in tears are red. Although the porphyrins in tears are too dilute to turn tears red, porphyrins can accumulate in the hair below the eyes over time as tears spill into it. The hair then turns red or red-brown.

Poodle with tear stains by Shutterstock.

As it turns out, only light-colored dogs develop tear stains. Or rather, only light-colored dogs develop tear stains that can be noticed by their owners. In some white breeds of dogs, such as the Maltese, tear stains are almost ubiquitous.

Like eye boogers, tear stains aren’t always a sign of trouble, but certain eye problems can result in excessive tear staining. Dogs may be predisposed to tear stains by any condition that causes the eye to produce excessive tears or any condition in which the nasolacrimal duct does not drain tears properly. Therefore, if your dog has tear stains, it’s best to have the vet check check him to make sure nothing bad is going on.

Tear stains themselves may be unsightly, but they are harmless. However, overflowing tears that cause the hair to be continuously wet also may cause secondary skin infections.

Many owners of white dogs become inordinately disturbed by their pets’ tear stains. As a result, a host of products exists to address the “problem.” With the exception of hydrogen peroxide, I have no objection to topical products designed to cleanse the fur (hydrogen peroxide is a major irritant, and I don’t recommend using it near the eyes). Some people recommend using distilled water, rather than tap water, to cleanse the areas below the eyes. I see no reason why distilled water should work better, but if it floats your boat then no harm will be done to your dog.

Be aware that one oral product that purports to prevent tear stains (and that is reputed to work well), Angel Eyes, contains tylosin. Tylosin is an antibiotic. Antibiotics are serious medications that can change the balance of bacteria in the intestines, on the skin, and elsewhere in the body. The consequences of such changes are poorly understood, but they may be far-reaching. I’m not a fan of giving dogs antibiotics to treat cosmetic issues, so in general I recommend against Angel Eyes.

Frankly, my final take on tear stains is that the best way to deal with them is to be tolerant of them. If tear stains really bother you, consider adopting a dog with black fur. My pal Buster has never had a (visible) tear stain in his life.

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