Eyes & Mouth Health Guide

Cause ① Excess Porphyrin (The Core Mechanism of Tear Staining)

• ✓The reddish-brown discoloration below the eyes is caused by porphyrin pigments in tears that oxidize when exposed to air and light. Porphyrins are normal metabolic by-products of red blood cell hemoglobin breakdown, excreted through tears, saliva, and urine.
• ✓Porphyrin production can increase due to inflammation, immune reactions, stress, and dietary components. Some food ingredients (excess iron, artificial colors, certain preservatives) have been reported to stimulate porphyrin production. Hand et al. (2010): dietary components can influence tear composition, but randomized controlled studies directly proving a causal link between specific ingredients and tear staining are still limited.
• ✓Breeds most affected by tear stains: white-coated small breeds — Bichon Frisé, Maltese, Shih Tzu, Poodle — show the most visible staining. These breeds also commonly have structural issues such as entropion (inward-rolling eyelids) or nasolacrimal duct stenosis that cause excessive tearing.
• ✓Dietary improvements may reduce symptoms, but if a structural cause (blocked tear duct, entropion) is present, veterinary treatment should come first. Infectious conjunctivitis or corneal ulcers accompanied by excessive tearing require immediate ophthalmic examination.

Cause ② Periodontal Disease (The Overwhelmingly #1 Cause of Bad Breath)

• ✓Niemiec (2013): periodontal disease affects more than 80% of dogs over 3 years of age. It is the most common cause of bad breath — left untreated, it progresses from plaque and tartar to alveolar bone loss, tooth loss, and bacterial spread to the heart and kidneys.
• ✓The anaerobic bacteria responsible for bad breath (Porphyromonas, Fusobacterium, etc.) thrive beneath tartar deposits, producing foul-smelling compounds including hydrogen sulfide and methyl mercaptan. These same bacteria are associated with infective endocarditis (heart valve inflammation).
• ✓Dietary factors: wet food and soft treats adhere easily to tooth surfaces, accelerating tartar formation. Dry food — especially VOHC (Veterinary Oral Health Council) certified dental diets — helps remove tartar through mechanical abrasion.
• ✓Improving bad breath requires more than dietary changes: daily tooth brushing, professional scaling (by a vet), and dental food/treats used together. Dietary changes alone cannot reverse moderate to severe periodontal disease.

Cause ③ Extra-Oral Causes (Kidney, Diabetes & Digestive Issues)

• ✓If bad breath appears suddenly or has a sweet/acetone smell or ammonia/urine odor, it may not be a simple oral issue. Sweet or fruity/acetone smell: possible diabetic ketoacidosis (DKA). Ammonia or urine smell: possible kidney dysfunction (uremia).
• ✓Gastrointestinal problems (reflux esophagitis, abnormal gastric fermentation) also cause bad breath. Frequent burping after meals combined with bad breath warrants a gastrointestinal workup.
• ✓Dietary note: foods high in fish ingredients may produce a fishy odor, but this is unrelated to oral disease. Incomplete protein digestion can worsen bad breath through abnormal intestinal fermentation.
• ✓If periodontal disease is absent but bad breath persists, ask your vet for blood tests (BUN, creatinine, blood glucose) to check for kidney disease or diabetes.