Health Topics  >  Dental and Oral  >  Bad Breath

What are common causes of bad breath in dogs?

The most common causes of bad breath in dogs are: 

  • Dental disease (tartar, gingivitis or a more serious issue like an abscessed tooth)
  • Oral foreign body (object lodged in the mouth somewhere causing infection)
  • Lip fold pyoderma (a type of skin infection), often associated with food allergies
  • Oral cancer
  • Gastrointestinal upset and vomiting causing bad breath
  • Ingestion of a malodorous item (dogs will be dogs!)


There are also many less common causes, for example kidney disease and diabetes mellitus can cause distinct odors of the breath. Each of the common causes are explained more below.

Periodontal or Dental Disease

Periodontal or dental disease occurs when plaque builds up on the teeth (both above and below the gumline), and is the most common cause of all dental diseases in dogs. Without regular tooth brushing (weekly if not daily for most dogs), plaque can become mineralized to form rough, brown tartar. This process eventually causes gingivitis or gum inflammation, and as it progresses, the teeth lose support, and the ‘good bacteria’ changes into ‘bad bacteria’. This is essentially the same process as what happens in humans.

In the worst cases, the teeth can rot from the inside out and dogs may even develop a dental abscess, a severe and painful infection that develops around the root of a tooth.

Periodontal disease is a common cause of bad breath. In more severe cases (as pictured here), the dog may be prone to other illnesses (ex. bacterial infection) as well.

Bad Eating Habits and Oral Foreign Bodies

Unpleasant dietary habits of eating food (and non-food items) from the ground, garbage diving, and eating decomposing animal remains all can cause foul breath.

Put simply, unsupervised snacking is a significant cause of bad breath. It’s also a major cause of toxin ingestion, so it’s a good habit to know what your dog is getting into. Paying close attention to the type of smell can give you clues about the cause of your dog’s bad breath.

Small bits of food and other objects can become lodged in the teeth or mouth and will eventually decay, causing an offensive smell. This includes shards of bone or pieces of wood that have broken off a stick.

The food you regularly feed your pup can also cause bad breath. Dry food is superior to wet food when it comes to maintaining healthy teeth and fresh breath. This is because wet food cakes the teeth and becomes a breeding ground for bacteria, while dry foods like kibble can help crack off both plaque and calculus.

Pro Tip: Dry food is better for maintaining healthy teeth and fresh breath in dogs than wet food.

Oral Ulcer or Lip Infection

An oral ulcer can have many causes including trauma, cancer and kidney disease. The ulcer appears as a sore on the lips, tongue, cheeks or gum and is usually painful. If there is a secondary infection caused by bacteria, your dog may also have bad smelling breath. 

Lip fold pyoderma is a common skin infection that develops in the skin fold on the outside of a dog’s mid-lower lip. It usually looks rusty red in color and can have pus or crusty discharge with a strong odor. It is most commonly caused by a food allergy (typically to a protein source in the dog’s diet, for example a chicken allergy). Dogs with lip fold pyoderma will often have other signs of itchiness such as licking their paws, prone to ear infections, or itchy bums.

Tumors Involving the Oral Cavity

Oral tumors can grow at an accelerated speed that can be difficult for the associated blood vessels to keep up with. As a result, oral tumours may develop pockets of dead tissue and abscesses of infection. These areas will cause a bad odor.

Somet oral tumors are visible, but they can be hidden in the oral cavity.

Gastrointestinal Issues

Dietary indiscretion can also cause nasty vomits that leave the mouth smelling bad. An imbalance in your dog’s gut or oral microbiome due to an overgrowth of the ‘bad’ intestinal bacteria can be linked with bad breath. In other cases, systemic issues such as a megaesophagus resulting in food pooling, can lead to bad breath.

Kidney or Liver Disease

Kidney failure, disease or other metabolic diseases can cause bad breath. When kidney functions decrease, toxins build up in the bloodstream and often manifest in bad breath, often smelling like ammonia or urine.

Metabolic disease that affects your dog’s breathing is a significant health issue and requires urgent veterinary attention. In extreme cases, dogs may be displaying other clinical signs such as chronic weight loss and vomiting.

Apart from kidney disease, liver disease can also cause bad breath. If you notice a foul smell accompanied by a lack of appetite, vomiting, and yellow gums, it may be a sign of liver disease, which also requires urgent vet attention. 

Pro Tip: If your dog experiences additional symptoms such as a lack of appetite, weight loss, vomiting, excessive itching and scratching or yellow-ish colored gums, these are signs of a serious underlying cause that requires urgent vet attention.


Dogs who have diabetes will have increased sugar content in their saliva, and sometimes results in a sweet or fruity smell in their breath – often resembling nail polish remover. In these cases, other symptoms such as drinking and urinating more will usually be present.