Why Does My Dog’s Breath Smell? Understanding Canine Halitosis

While it’s common, bad breath (halitosis) in dogs isn’t just about smell. It’s usually a reflection of what’s happening inside your dog’s mouth, and sometimes elsewhere in the body. The underlying cause might be as simple as dental tartar build-up or as complex as a systemic illness.

Why Does My Dog’s Breath Smell?

Every dog’s mouth is home to millions of microorganisms that make up the oral microbiome - a balanced community that helps protect the gums and teeth. When this balance is disturbed, harmful bacteria multiply and produce volatile sulphur compounds (VSCs), which are responsible for unpleasant odours.

This shift, called dysbiosis, is often triggered by plaque and tartar accumulation, gum inflammation, periodontal disease or an underlying systemic disease.

Does Plaque Smell? Or Is It Periodontal Disease?

Plaque itself doesn’t have a strong smell when it first forms. It’s mostly made of saliva proteins and harmless bacteria. But if it’s not brushed or wiped away within a day or two, the environment inside that plaque changes.

As oxygen levels drop, anaerobic bacteria (the kind that thrive without oxygen) begin to dominate. These bacteria break down proteins in saliva and food particles, releasing sulphur-based gases and the first hint of “doggy breath.”

Once plaque hardens into tartar, it traps more bacteria under the gumline, creating the perfect environment for infection and inflammation. This is known as periodontal disease. 

At this stage, the smell becomes much stronger and more persistent because of bacterial toxins, pus, and ongoing tissue breakdown.

So, while early plaque may cause only a mild odour, it’s periodontal disease and bacterial overgrowth that cause the truly unpleasant smell associated with dental disease. You can read more about periodontal disease here.

Common Causes of Bad Breath in Dogs

1. Dental and Gum Disease — The most common cause of bad breath. Plaque and tartar shift the oral microbiome toward bacteria that release foul-smelling sulphur compounds. Over time, this leads to gingivitis and periodontal disease, which can cause pain, infection, tooth loss, jaw bone damage, and potentially systemic effects.
2. Food and Chewing Habits — Dogs that scavenge or eat unusual things (such as compost, poop, or decaying material) can develop a temporary odour from their mouth, nose and hair on the muzzle.
3. Oral Infections or Foreign Objects — A stick, grass seed, piece of bone or any other foreign material caught between the teeth or under the gum can cause local irritation, infection and abscessation, resulting in an unpleasant smell from the area.
4. Underlying Health Conditions — Sometimes, bad breath reflects an illness elsewhere in the body:
   • Kidney disease: Breath may smell like ammonia or urine.
   • Diabetes with increased ketones: Can cause a sweet or fruity smell breath.
   • Liver disease: Can lead to a musty or metallic odour, often accompanied with yellowing gums and eyes.
   • In these cases, the change in smell often coincides with other symptoms, such as lethargy, changes in appetite, vomiting, diarrhoea, increased thirst, changes in urination and other signs of being unwell.

Screening Tests for Other Causes

When investigating bad breath, your vet may recommend tests to identify or rule out broader health problems. This can include:

• Blood tests
• Urine tests
• Dental X-rays
• Abdominal ultrasound 
• CT Scan
• Oral examination under anaesthesia - this allows full inspection of the gums, tongue, and throat without discomfort.

These tests ensure that bad breath isn’t just treated as a “mouth issue” when it may be linked to a systemic cause.

How to Fix and Prevent Bad Breath Caused by Dental Disease

1. Professional Dental Cleaning — If tartar or gum disease is present, a professional veterinary dental clean under general anaesthesia is the only way to remove bacteria and plaque below the gumline. This also helps to restore a healthy oral microbiome. Pre-anaesthetic blood tests are recommended to screen for underlying illnesses to assess the risk of anaesthesia.
2. Daily Home Dental Care — Brushing or wiping your dog’s teeth can remove plaque before it hardens into tartar. Daily cleaning helps maintain a healthy oral bacterial balance and prevents odour. Creating an evening routine to clean the teeth after dinner is a great place to start. Read our full guide here: How to Clean Your Dog’s Teeth.
3. Dental Chews and Toys — Chews can reduce soft plaque, but are not a replacement for brushing or wiping. Look for veterinary-approved products and choose softer chew toys that won’t damage teeth.
4. Nutrition and Hydration — A complete and balanced diet supports both oral and systemic health. Offer free access to clean water throughout the day, and after meals to help rinse away food particles.

The Microbiome Beyond the Mouth

Periodontal disease and an unbalanced oral microbiome can affect more than just your dog’s breath. Bacteria from the mouth can enter the bloodstream and influence the health of vital organs such as the heart, liver, and kidneys. So maintaining dental hygiene protects not just oral health, but overall wellbeing.

When to See Your Vet

Book a checkup if your dog’s breath:

• Smells persistently bad or suddenly changes
• Is accompanied by signs such as, discoloured teeth, red or bleeding gums, drooling, or difficulty eating
• Comes with any other signs of illness 
• Hasn’t improved with regular brushing or wiping 
• Early diagnosis and intervention can make a huge difference - both for comfort and long-term health.

A Healthy Mouth Means a Healthier Dog

Bad breath is more than a funky smell - it’s a signal. It might be telling you that your dog’s oral microbiome is unbalanced, plaque and tartar are building or periodontal disease has begun. It may also be caused by another disease process in the mouth or secondary to a systemic illness. 

By combining vet checks, daily teeth cleaning, and the right nutrition, you can help keep your dog’s mouth (and whole body) healthy.