visibilityEyes & Mouth
Eyes & Mouth Health Guide
Tear stains and bad breath are not just cosmetic issues — they reflect dietary components and oral health status. The right food choices and care habits can make a real difference.
Detailed Guides
Select the guide that matches your dog's symptoms.
Eyes & Mouth
Tear Stains
Learn about the dietary factors behind reddish-brown tear staining caused by porphyrin pigments, and improvement strategies for white-coated breeds.
Eyes & Mouth
Bad Breath
Understand how dietary factors contribute to bad breath, and find food and treat selection criteria that support oral health and tartar management.
80%+
of dogs over 3 years have periodontal disease
Porphyrin
oxidized tear pigment — the cause of staining
VOHC
standard for dental food & treat certification
3 Key Causes of Eye & Mouth Health Problems
Periodontal disease affects more than 80% of dogs over 3 years. Left untreated, it goes beyond bad breath — bacteria can spread to the heart, kidneys, and liver.
Excess Porphyrin (The Core Mechanism of Tear Staining)
Porphyrin
oxidized tear pigment causing reddish-brown stains
Porphyrin
oxidized tear pigment causing reddish-brown stains
- check_circleThe 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.
- check_circlePorphyrin 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.
- check_circleBreeds 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.
- check_circleDietary 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.
Periodontal Disease (The Overwhelmingly #1 Cause of Bad Breath)
80%+
of dogs over 3 years have periodontal disease (Niemiec 2013)
80%+
of dogs over 3 years have periodontal disease (Niemiec 2013)
- check_circleNiemiec (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.
- check_circleThe 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).
- check_circleDietary 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.
- check_circleImproving 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.
Extra-Oral Causes (Kidney, Diabetes & Digestive Issues)
VOHC
certification standard for dental health products
VOHC
certification standard for dental health products
- check_circleIf 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).
- check_circleGastrointestinal problems (reflux esophagitis, abnormal gastric fermentation) also cause bad breath. Frequent burping after meals combined with bad breath warrants a gastrointestinal workup.
- check_circleDietary 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.
- check_circleIf 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.
Find the Cause by Symptom
Emergency symptoms in the table below require immediate veterinary attention.
| Symptom | Suspected Cause | Guide |
|---|---|---|
| Reddish-brown discoloration below eyes (especially on white coats) | Porphyrin pigment + possible dietary component | → Tear Stains Guide |
| Excessive tearing + discharge, redness | Ocular disease (conjunctivitis, keratitis) | Immediate vet exam needed |
| General bad breath, yellowed tartar | Periodontal disease (plaque/tartar accumulation) | → Bad Breath Guide |
| Sweet or acetone-like breath smell | Possible diabetic ketoacidosis (DKA) | Immediate vet exam needed |
| Ammonia or urine-like breath smell | Possible kidney dysfunction (uremia) | Immediate vet exam needed |
If tearing increases suddenly, or is accompanied by discharge or redness, it may indicate an ocular disease. If bad breath is severe, gums are swollen or bleeding, or the breath smells sweet or ammonia-like, seek immediate veterinary care. The information on this page is for general educational purposes only and does not replace veterinary advice.
References
- Niemiec, B.A. (2013). Periodontal disease. Top Companion Anim Med, 23(2), 72–80.
- Hand, M.S. et al. (2010). Small Animal Clinical Nutrition, 5th ed. Mark Morris Institute.
- Harvey, C.E. (2005). Management of periodontal disease: understanding the options. Vet Clin North Am Small Anim Pract, 35(4), 819–836.
- VOHC. (2023). Veterinary Oral Health Council accepted products for dogs.