By Dr. Patrick Mahaney, VMD
Have you ever seen a white dog who looks like he’s crying all the time, or a white dog with a dark, stained beard? These pooches often seem to have a pink to brown beard. This can happen to any part of your dog’s body that he likes to lick or chew, such as the fur on your dog’s feet or the fur around the eyes. While it’s harmless for the most part, there are some medical conditions that could cause excessive staining in your dog’s fur.
Why Are These Areas a Different Color?
Saliva and tears contain substances called porphyrins, which stain light fur pink, red or brown.
Porphyrins are organic, aromatic compounds that make up many important structures in the body. The term porphyrin comes from the Greek word πορφύρα (porphura), which translates as ‘purple.’ Although I have never seen a pet with a purple beard, feet or tear tracts, the staining often starts out as a dark pink-purple hue that gradually becomes brown as time goes on and more porphyrins are applied.
Is It Normal for These Areas to Undergo Color Change from Porphyrin Staining?
Yes and no, as there are certain locations that will be invariably stained by the presence of porphyrins. It’s quite natural for the beard to undergo color change, as saliva originates in the mouth and some of it is bound to end up on the lip and mouth.
A normally functioning eye produces tears to lubricate the eyeball so that the eyelids don’t stick to it. A small amount of staining from natural tear production can be expected, but a prominent tear-tract from the inner or outer edge of the eyelids is abnormal.
The skin and fur on the feet, knees and other body parts are also not locations where tears or saliva would naturally appear. Have you noticed your dog constantly licking the same spot? There may be a primary health problem causing staining in these areas.
What Underlying Health Problems Contribute to Porphyrin Staining?
Yes, there are a variety of health problems, some mild and others severe, that can contribute to excessive accumulation of porphyrins on bodily surfaces.
- Periodontal disease- Pets with periodontal disease have higher levels of bacteria in their mouths. As a result, more saliva is produced in attempt to rid the bacteria from being absorbed through the gums into the bloodstream. Periodontal infections such as tooth abscesses can also create the sensation of nausea and cause drooling.
- Conformational abnormalities- If your pet can’t properly close his mouth or if he has unnecessary skin folds in his lips, saliva can exit the mouth and accumulate on the hair around your dog’s mouth.
- Difficulty chewing food- Problems chewing food can cause saliva to be unevenly distributed in the mouth and trickle down the sides of the mouth. Chewing difficulties are commonly associated with periodontal disease, fractured teeth, and oral tumors.
- Inflammation- Environmental irritation from seasonal or non-seasonal allergies can cause inflammation of the various eye structures and lead to excessive tear production.
- Conformational abnormalities- Abnormally placed eyelashes (ectopic cilia and distichaisis), rolling in of the eyelids (entropion), tear duct obstructions, and other conditions can cause soft or rigid hairs lining the eyelids to touch the eyeball and create inflammation and extra eye discharge.
- Infection- Bacteria, fungi, parasites, and viruses all have the ability to infect the eye and lead to the production of excess tears as the body tries to flush them out.
- Cancer- Cancer that affects the eye can cause abnormal positioning of the eyeball within the socket, enlargement of the globe (buphthalmia), or other changes that can affect the normal tear drainage from the eye.
- Trauma- Injuries from an object or abrasion from a pet’s paw can damage the surface of the eye (corneal ulcer) and lead to increased tear production.
- Inflammation- Seasonal and non-seasonal environmental and food allergies can cause a pet to lick or chew on the feet, knees, or other body parts. Inflammation can also be caused by items embedded in the skin, painful joints, flea bites, etc.
- Infection- Bacterial, fungal, or even parasitic infection of the skin can motivate our pets to strive to resolve the issue themselves by licking or chewing.
What Should You Do If You Note Brown Staining to Your Dog’s Beard, Eyes or Other Body Parts?
It’s best that dogs showing excessively stained body parts have an examination by a veterinarian to look for potential underlying health problems. As there are so many potential causes of porphyrin staining, each option and the pet’s whole-body health must be carefully considered when determining the appropriate diagnostic testing and treatment.
Pending the veterinarian’s evaluation and ability to manage the issue, an affected pet may need to be evaluated by a veterinary specialist, such as an ophthalmologist, dermatologist, dentist or internal medicine specialist.