Eye stains in dogs are caused by porphyrin, a compound in tears that results from red blood cell breakdown. Normally eliminated through the liver and faeces, porphyrin can also be found in a dog’s tears, saliva, and urine. Porphyrin is an iron-based compound that breaks down to leave a reddish mark on dogs exposed to sunlight. This is why dog tear stains are particularly prominent in white or light-coloured dogs. It is important to note that there is no correlation between dog tear stains and the production of tears itself- as all tears contain porphyrin.
While excessive tearing could be due to breed predisposition, that is not always the case. Conditions such as allergies, tooth pain, stress, and infections (eye and/or ear) could cause excessive tearing. If you notice redness, inflammation, or any abnormalities in your dog’s eyes, it is best to have them checked by a veterinarian.