Why does my dog's breath smell so bad

Last updated October 14, 2026

Most bad breath in dogs starts in the mouth. Bacteria living in plaque, in the pockets around the teeth and on the back of the tongue break down proteins and give off sulfur gases, and the more inflamed the gums, the stronger the smell. Strong breath isn't normal dog breath, even in an older dog.

A few smells point somewhere else. Breath that smells sweet, like ammonia, or like poop in a dog that is vomiting needs a vet soon, sometimes the same day. For the usual rotten-egg smell, the fix is cleaning the mouth rather than covering the odor, and tartar that has already hardened on the teeth needs your vet before home care can keep breath fresh.

Where the smell comes from

The odor is mostly hydrogen sulfide and methyl mercaptan, two volatile sulfur compounds. A 1998 review by Culham and Rawlings in the Journal of Veterinary Dentistry traced them to Gram-negative bacteria in plaque, in gum pockets and on the tongue, and noted the same gases are thought to play a part in gum disease itself. Porphyromonas gulae, thought to be the main bacterium behind periodontal disease in dogs, produces large amounts of both gases in the lab (Ito and colleagues, 2023).

Illustration of a bacterial biofilm coating a tooth, the plaque layer where the bacteria behind bad breath live

That's why breath tracks the gums so closely. In a small 1997 study of beagles, a trained panel picked out the dogs with gum disease by breath alone, and the strength of the smell rose with gum inflammation and with bone loss between the roots. The same authors point out that not every dog with bad breath has gum disease, which is why the type of smell matters.

You can check this at home by smelling your dog's breath first thing in the morning, before breakfast. Rawlings and Culham found that dogs producing a lot of these gases smelled worst early in the day, while dogs brushed daily from a young age stayed low and steady.

What different smells can mean

Smell decoder graphic with five dog breath smells: fishy, metallic, earthy, sweet and foul

Smell What it often means What to do
Rotten eggs, cheese, garbage Plaque bacteria and early gum disease, the most common cause Start daily home care and book a dental check
Rotten and very strong, with drooling, pawing at the mouth or not eating Advanced gum disease, a tooth root abscess, a stick or grass awn stuck in the mouth, or a growth Vet within a few days
Metallic, like blood Bleeding gums, a cut in the mouth, a broken tooth, or a mouth tumor that has ulcerated Lift the lip and look, then see your vet
Fishy Fish-based food, or licking the rear end when the anal sacs are full If your dog scoots or licks its bottom, have the anal sacs checked
Poop, dog otherwise well Usually means your dog has eaten poop Clean up the yard
Poop, with vomiting, a swollen belly or lethargy Something more serious in the gut Vet the same day
Ammonia or urine Kidney disease is one cause Vet soon for blood and urine tests
Sweet, fruity, like nail-polish remover Can be diabetes, where ketones build up Vet soon, the same day if your dog is weak, vomiting or off food

Wheel of dog breath smells by how soon to act: fishy or rotten-egg smells mean home care and a dental check, rotten with drooling or metallic means a vet this week, sweet, fruity or poop-like with illness means a vet today

The body-wide causes come with other signs, and those usually tell you more than the smell does. The Merck Veterinary Manual lists more drinking and peeing as the earliest signs of chronic kidney disease, and later a poor appetite, weight loss and mouth sores. Diabetes brings more thirst, more urination and weight loss despite a good appetite. Once ketones build up, a dog becomes weak and lethargic and may struggle to breathe, which is an emergency.

Outline of a dog with the kidneys and stomach highlighted, labelled stinky breath often has deeper roots. Body-wide causes are possible, but most bad breath starts in the mouth

Mouth tumors are easy to blame on teeth. Merck lists bad breath, reluctance to eat and heavy drooling as common signs, so any lump on the gums gets a vet visit.

Clean-looking teeth can still be the problem

In a 2018 study in the Journal of the American Animal Hospital Association, 114 dogs had a look-in-the-mouth exam while awake, then a full exam with probing and dental x-rays under anesthesia. The awake exam underestimated both how many dogs had active gum disease and how bad it was.

So if the breath is bad and the teeth look white, it's still worth a dental check. Red gums along the tooth edge are gingivitis, the stage that a cleaning and daily care can still turn around. Our guide to gingivitis and periodontitis in dogs explains the stages.

A vet cleaning works on breath even in old dogs. Rawlings and Culham found that periodontal treatment cut bad breath substantially and kept it below the starting level for up to three months. The order matters, so a professional cleaning comes first and home care follows. Scaling an awake dog isn't a shortcut. The American Veterinary Dental College says the part below the gumline can't be cleaned without anesthesia, and the 2026 WSAVA dental guidelines call anesthesia-free dentistry "ineffective at best and damaging at worst".

How to make your dog's breath smell better

Brushing is the method with the clearest evidence. When Enlund and colleagues (2024) brushed 22 beagles daily, the sulfur compounds and plaque both fell within the first week. Two weeks after brushing stopped, plaque and gum scores were back where they started. In an earlier beagle trial, brushing every other day still gave clearly better results than brushing once a week (Harvey and colleagues, 2015). Use dog toothpaste only.

Ledger of what studies found changes dog breath: daily brushing within a week, a vet cleaning for up to three months, seaweed dental bites at 90 days, and no dog trial found for parsley, mint or coconut oil

If your dog won't accept a brush, chews, water additives and dental diets can help. The Veterinary Oral Health Council awards its seal in two categories only, plaque and tartar. There is no seal for breath, so a "fresh breath" line on a pack hasn't been tested to that standard. Look for the plaque or tartar seal instead, since less plaque is what lowers the smell. Our guide to cleaning dog teeth without brushing compares the options.

Seaweed is another option with a trial behind it. In Gawor and colleagues' 2018 study, 60 small-breed dogs had their teeth cleaned and then ate dental bites containing Ascophyllum nodosum, a brown seaweed, or a placebo bite for 90 days. Breath sulfur compounds ended about 46% lower in the seaweed group. That 46% is the breath figure. Plaque was about 38% lower. The trial was paid for by the maker of the bites, and only small dogs took part.

Caniclean is our seaweed powder. You sprinkle it on your dog's food, and it helps reduce plaque and new tartar. It won't lift tartar that is already hard, and it isn't VOHC-accepted. Seaweed contains iodine, so check with your vet first if your dog has a thyroid condition, takes thyroid medication or has kidney disease. One customer wrote in a verified review on January 16, 2024, "Not only does it make my dogs breath smell great!"

Natural remedies, and what they can't do

Kitchen remedies can mask breath for a while, but we couldn't find a controlled trial in dogs showing that any of them reduces plaque. Use them alongside cleaning.

  • Coconut oil is popular for brushing. There's no dog trial behind it, and it's high in fat, so keep amounts small and ask your vet first if your dog has had pancreatitis.
  • Carrots and apple slices make good low-calorie snacks. Take out the core, since apple seeds contain cyanide compounds, and cut carrots into pieces a gulper can't choke on.
  • A pinch of chopped curly parsley on food can mask odor. The ASPCA lists parsley as toxic to dogs in large amounts (it can cause sunburn-like skin reactions), so a pinch is fine and a daily handful isn't.
  • Plain yogurt is fine as a treat if the label has no xylitol. It won't change sweet-smelling breath, which needs a vet.

The chart below sorts foods by safety. Where it says "effective", read it as freshening breath for a while, not cleaning teeth.

Cheat sheet of breath-freshening foods. Carrots, apple flesh, curly parsley, mint and plain yogurt are listed as safe to offer, and onions, garlic, spring parsley and xylitol as foods to avoid

Some popular fixes are unsafe. Human toothpaste can contain xylitol, which the Merck Veterinary Manual says can cause a dangerous drop in blood sugar and, less often, liver damage. Garlic and onion damage a dog's red blood cells, whether raw, cooked or powdered. Baking soda isn't a toothpaste substitute either.

Terrier licking a small amount of coconut oil from its owner's finger

When to see a vet

These signs need a vet, not more home care.

  • Bad breath that doesn't improve after two or three weeks of daily care
  • A sudden change in breath, especially in an older dog
  • Brown or yellow crust at the gumline that doesn't wipe off
  • Red, swollen or bleeding gums, or a loose or broken tooth
  • Drooling, pawing at the mouth, chewing on one side or dropping food
  • A lump on the gums, or swelling on the face or under an eye, which can be a tooth abscess
  • Drinking or peeing more, weight loss, or yellow gums or eyes

Go the same day if bad breath comes with vomiting, a swollen belly, weakness or refusing food.

Questions owners ask

Is it normal for a dog's breath to smell?

A mild smell after eating is normal. Breath you notice from across the room, or that makes you turn away, usually means plaque and gum inflammation, and it's worth a check.

How can I freshen my dog's breath naturally?

Brush with dog toothpaste daily or every other day, and add a chew, water additive or seaweed if brushing is hard. Parsley and similar remedies only mask the smell for a while.

Why does my old dog's breath suddenly smell so bad?

Older dogs build up more gum disease, and a sudden change can mean an abscess, a broken tooth, a growth or a kidney problem. A vet visit sorts out which.

Can bad breath in dogs be a sign of kidney disease?

Yes. Breath that smells like ammonia or urine can come from kidney disease, usually with more drinking and peeing. It needs blood and urine tests.

References

  • American Veterinary Dental College. Companion animal dental scaling without anesthesia (position statement). avdc.org.
  • ASPCA Animal Poison Control Center. Parsley (Petroselinum crispum); Apple. aspca.org.
  • Culham N, Rawlings JM. Oral malodor and its relevance to periodontal disease in the dog. J Vet Dent. 1998;15(4), 165-168.
  • Enlund KB, Rahunen N, Thelander S, Olsén L. Evaluation of a thiol-detection test to assess tooth brushing efficacy in dogs. J Vet Dent. 2024;41(3), 183-191.
  • Gawor J, Jank M, Jodkowska K, Klim E, Svensson UK. Effects of edible treats containing Ascophyllum nodosum on the oral health of dogs. Front Vet Sci. 2018;5, 168.
  • Harvey C, Serfilippi L, Barnvos D. Effect of frequency of brushing teeth on plaque and calculus accumulation, and gingivitis in dogs. J Vet Dent. 2015;32(1), 16-21.
  • Ito N, Itoh N, Kameshima S. Volatile sulfur compounds produced by the anaerobic bacteria Porphyromonas spp. isolated from the oral cavities of dogs. Vet Sci. 2023;10(8), 503.
  • Merck Veterinary Manual. Disorders of the mouth in dogs (updated June 2026); Noninfectious diseases of the urinary system in dogs (updated May 2026); Disorders of the pancreas in dogs (updated May 2026); Disorders of the rectum and anus in dogs; Xylitol toxicosis in dogs (updated June 2025); Garlic and onion (Allium spp) toxicosis in animals (updated September 2024). merckvetmanual.com.
  • Niemiec B, Gawor J, Nemec A, et al. World Small Animal Veterinary Association global dental guidelines. J Small Anim Pract. 2026. doi:10.1111/jsap.70057.
  • Queck KE, Chapman A, Herzog LJ, et al. Oral-fluid thiol-detection test identifies underlying active periodontal disease not detected by the visual awake examination. J Am Anim Hosp Assoc. 2018;54(3), 132-137.
  • Rawlings JM, Culham N. Studies of oral malodor in the dog. J Vet Dent. 1998;15(4), 169-173.
  • Simone AJ, Logan EI, Livgren R, Suelzer M. Oral malodor in beagles, association with indicators of periodontal disease. J Clin Dent. 1997;8(6), 163-168.
  • Veterinary Oral Health Council. Protocols and submissions. vohc.org.