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What Causes Tear Stains in Dogs?: The Science of Tear Stains

Small dog on a white background.
Small dog on a white background.

When it comes to dogs' tear stains, most of the products available address bleaching and/or removing the tear stain but not eliminating the reason for the tear stains. Some vets like to say tear stains are natural in certain dogs and many vets even say there is no known explanation.  Perhaps that’s because there is no convenient explanation for what causes tear stains.  There is a scientific explanation for what causes tear stains and this blog is all about science.  
(Not interested in this scientific stuff but still want to know more? TEAR STAINS)

If you’ve done any research about tear stains on dogs you might have heard about Epiphora: excessive tear production. 

Scientific formula showing tear stains.

If you’ve dug deeper into tear stains you might have heard about porphyrins.  

The red/rusty stains on your dog are tear stains caused by porphyrins. Porphyrins are commonly called waste products from red blood cells containing iron. 

Porphyrins are created during the normal cycle of biosynthesis of hemoglobin to create energy. They are created in humans, too. Every day, red blood cells are naturally broken down in the body during Krebs cycle which produces CO2 and generates energy molecules.

This is known as heme biosynthesis. During this cyclic process, a chemical substance known as porphyrin is left in the body and excreted. Excreted thru the liver, it becomes part of bile. It can be part of urine or in this case, tear stains.

The cycle: Glycine & Succinyl CoA is needed for heme biosynthesis to begin. 

Scientific model showing tear stains.

Aminolevulinic acid - ALA - is the catalyst. Pyriodxal phophate (B6) and ALAS1 (Aminolevulinic Acid Synthase) are needed to convert Glycine and succinyl CoA to ALA. Condensation with Succinyl CoA takes place while the amino base glycine is in schiff base linkage to the aldehyde of Pyriodxal phosphate (B6) and it converts Succinyl CoA to ALA Heme itself, then acts as a feedback inhibitor to ALA and ALAS1 ALAS1 is one of the co-factors needed for the liver's housekeeping, removal of overall accumulation of toxic metabolics.

A model showing glycine-PLP.

Medically speaking, Porphyrias; which would be indicated by excess Porphyrins – red/rusty tear stains, is the condition which results when there are specific enzyme deficiencies in the heme synthesizing pathway.  This is when the co-factors are not present to stop  the cyclic process.

Small dog in a field, running towards the camera.
Small dog in a field, running towards the camera.

The most common triggers of excess of Porphyria are Sulfonomides. Sulfonomides are FDA approved bacteriostatic chemicals.  Sulfonamides are frequently used in pigs, cattle and chicken for the treatment and prevention of bacterial diseases. Sulfonamides (sulfa drugs) Sulfonamides are produced by chemical synthesis. They have bacteriostatic activity against a broad spectrum of pathogens. They interfere with RNA and DNA, which are necessary for cell growth and replication. If you and your dogs are not eating organic meat and your dog has symptoms of excess Porphyria switching to 100% Organic Dehydrated Dog Food will help.

If your dog’s tear stains are smelly. Chances are, there is also yeast imbalance. 
You can read more about yeast imbalance here.   

Special thanks to the following: 

More reading: If you are wondering what other drugs you are “eating”:

What farmers, FDA and Watch Groups think about anti-biotics and food:


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