What Causes Bad Breath in Dogs? Causes and When to Worry

Most bad breath in dogs starts in the mouth. A veterinary guide from VCA Canada, co-written by a board-certified veterinary dentist, names periodontal disease as the most common cause: bacteria in plaque and tartar along the gum line break down food debris and tissue and release smelly sulphur compounds. Less often, bad breath comes from an oral tumour or a bleeding problem.

The short version

• Usually gum disease: plaque bacteria and tartar along the gum line are the most common cause.
• It starts early: plaque begins forming again as soon as teeth are cleaned, and hardens into tartar within days.
• Small dogs are more prone, along with flat-faced breeds and spaniel types.
• New or worsening bad breath is a reason to see your vet, especially with other signs in the mouth.
• Daily plaque control helps, and the Veterinary Oral Health Council lists products shown to reduce plaque or tartar.

The usual cause: plaque, tartar and gum disease

Plaque is a film of bacteria that starts forming on a freshly cleaned tooth as soon as a dog salivates. According to VCA Canada, it mineralizes within days into rough tartar, which collects more plaque and inflames the gums. As gingivitis progresses into periodontitis, the loss of the tissue that holds teeth in place, the bacterial community shifts toward the kinds that produce foul-smelling compounds.

It can start young. In a 2019 study of Yorkshire Terriers, 98% of the 49 dogs had early periodontitis on at least one tooth by 37 weeks of age, about eight and a half months, and the odds rose with age. The researchers described periodontal disease as the most common oral disease of dogs.

Why small dogs are more prone

A 2021 study of 22,333 dogs under UK primary veterinary care found that 12.5% were diagnosed with periodontal disease in a single year, and the risk varied a lot by type of dog:

VCA Canada adds that small and flat-faced breeds are prone because their teeth sit closer together. If you have a small dog, our guide to a daily dental routine is a good place to start.

Other causes of bad breath

The same VCA Canada guide lists the main sources of bad breath:

• bacteria associated with plaque and tartar;
• food particles that rot in the pockets around diseased teeth;
• persistent bleeding from a clotting problem;
• tissue breakdown from a tumour in the mouth.

Because not every cause is dental, bad breath that doesn't improve with good dental care deserves a proper exam.

When bad breath means a vet visit

See your vet if your dog's bad breath is new, getting worse, or comes with any of these:

• red, swollen or bleeding gums, or visible brown or tan buildup on the teeth;
• a loose, broken or discoloured tooth;
• drooling, pawing at the mouth, dropping food or chewing on one side;
• a lump, sore or swelling in or around the mouth;
• other changes, such as eating less or losing weight.

The American Animal Hospital Association's dental guidelines warn that untreated periodontal disease can lead to chronic pain. A proper dental cleaning removes tartar above and below the gum line and is done under general anaesthesia, with X-rays to check the roots.

Daily habits that help

• Brush if your dog will let you. Daily plaque control is the core of preventing bad breath from coming back, VCA Canada notes.
• Choose tested products. The Veterinary Oral Health Council's accepted-products list names dental chews, diets and water additives that met its plaque or tartar standards.
• Keep up with checkups, so your vet can spot tartar and gum changes before they become painful.

Our oral microbiome hub explains what lives in a dog's mouth, and our guide to whether a dog's mouth is cleaner than a human's covers what that means for people.

Can a DNA test explain bad breath?

No. An oral microbiome section in a DNA kit describes the bacteria measured in one saliva sample; it doesn't examine teeth or gums. The PuppyGenes oral microbiome section does not diagnose or rule out dental disease, so bad breath is a question for your vet. Our guide to what an oral microbiome test can and can't tell you explains the difference.