Bad breath in dogs is usually caused by dental disease — plaque and tartar buildup, gum disease, or a developing infection — but it can also point to diet, an underlying digestive issue, or in some cases a more serious health condition. Occasional mild breath is normal, but persistent or suddenly worse breath is worth investigating rather than just masking with a chew or spray.
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Dental Disease: The Most Common Cause
The vast majority of bad breath in dogs comes down to their teeth and gums. Plaque builds up on the teeth constantly, and if it isn't removed, it hardens into tartar, which harbours bacteria and irritates the gums. Left unaddressed, this can progress to gum disease (periodontal disease), which is a genuinely common condition in adult dogs and a major cause of persistent bad breath.
Signs that dental disease is the likely cause include visible tartar (a yellow-brown buildup at the gum line), red or swollen gums, and reluctance to chew on one side of the mouth.
Other Common Causes of Bad Breath
Diet
What your dog eats can genuinely affect their breath — wet food tends to leave more residue in the mouth than dry kibble, and certain treats or table scraps can contribute to a stronger odour. This alone doesn't usually explain persistent bad breath, but it can make an existing dental issue smell worse.
Digestive Issues
Ongoing digestive upset, reflux, or a food intolerance can sometimes contribute to bad breath, particularly if it's accompanied by other symptoms like gas, loose stools, or vomiting.
Foreign Objects
Something lodged between the teeth or in the mouth — a splinter, a piece of stick, or food debris — can cause a sudden, sharp change in breath odour, often alongside excessive drooling or pawing at the mouth.
Kidney or Liver Disease
In more serious cases, bad breath can be a sign of an underlying organ issue. Kidney disease in particular can cause a distinctive ammonia-like smell, while liver disease can cause a different, often described as musty, odour. These are usually accompanied by other symptoms like increased thirst, lethargy, or appetite changes.
Diabetes
Uncontrolled diabetes can cause a sweet, almost fruity-smelling breath, caused by a build-up of ketones. This is usually accompanied by other symptoms like increased thirst and urination.
What the Smell Itself Can Tell You
| Type of smell | Possible cause |
| Generally unpleasant, "doggy" odour | Plaque, tartar, or early gum disease |
| Sharp, rotten smell | Advanced gum disease, infection, or a foreign object |
| Ammonia-like smell | Possible kidney issue — worth a vet check |
| Sweet or fruity smell | Possible diabetes — worth a vet check |
| Sudden change with no other cause found | Worth investigating diet or an underlying condition |
This table is a general guide, not a diagnosis — any persistent or unusual smell is worth mentioning to your vet, who can examine your dog's mouth and rule out or confirm the likely cause.
What to Do About It
- Check your dog's mouth for visible tartar, redness, swelling, or anything lodged between the teeth.
- Start or improve a dental care routine — regular brushing with a dog-specific toothpaste is the single most effective thing most owners can do.
- Consider dental chews or water additives designed to reduce plaque, as a supplement to brushing rather than a replacement for it.
- Book a dental check-up if it's been a while, since some dogs need a professional clean under anaesthetic once tartar has built up significantly.
When to See a Vet
Contact your vet if:
- The breath is suddenly or severely bad, rather than a gradual change.
- You notice red, swollen, or bleeding gums.
- Your dog is reluctant to eat or chews only on one side of their mouth.
- Bad breath is accompanied by increased thirst, urination, lethargy, or weight loss.
- You notice an ammonia-like or unusually sweet smell specifically.
Preventing Bad Breath in the Future
- Brush your dog's teeth regularly, ideally daily, with a dog-specific toothpaste — human toothpaste isn't safe for dogs.
- Provide dental chews designed to help reduce plaque and tartar buildup between brushings.
- Schedule regular veterinary dental check-ups, so any buildup or early gum disease is caught before it becomes a bigger problem.
- Feed a balanced, high-quality diet, and investigate further if you suspect a food intolerance is contributing to digestive-related breath changes.
FAQs
Can bad breath in puppies be normal?
Puppies going through teething can have temporarily unusual breath, but persistent bad breath still isn't something to ignore — check for retained baby teeth or gum irritation, and mention it to your vet at their next check-up.
Do dental chews actually work for bad breath?
They can genuinely help reduce plaque buildup as part of a routine, but they're not a substitute for brushing or for addressing an underlying dental or health issue if one exists.
Is it safe to use human mouthwash or toothpaste on a dog?
No — human oral care products often contain ingredients like xylitol or fluoride that are unsafe for dogs. Always use a product made specifically for dogs.
Bad breath is rarely something to just live with — in most cases it's a sign of a dental issue that's genuinely worth addressing, both for your dog's comfort and because untreated gum disease can affect their broader health over time. If the cause isn't obviously dental, it's worth ruling out diet, digestion, or an underlying condition with your vet.
If you suspect diet is playing a role, our Ultimate Pet Food Sensitivity Test checks 1,100 food, additive, and environmental items, helping you rule food in or out as a contributing factor.
To provide you with technically accurate, evidence-based information, content on the My Pet Sensitivity blog is reviewed by medical professionals with veterinary expertise.
Related reading: Top 10 Signs Your Dog May Be Sick