Is a Dog's Mouth Cleaner Than a Human's? What Science Says

No. A dog's mouth isn't cleaner than a person's; it's different. A 2012 study of the canine oral microbiome identified 353 kinds of bacteria in dogs' mouths and found that only about 16% of them are shared with human mouths. Both species carry bacteria that are normal in their own mouths but can cause infection somewhere else, such as in a bite wound.

The short version

• Not cleaner, different: dog and human mouths host largely different bacteria.
• Hundreds of kinds: researchers identified 353 bacterial groups in dogs' mouths, most of them unnamed at the time.
• Little overlap: only about 16% of dogs' oral bacteria matched those found in people.
• Licks are usually harmless, but dog saliva carries bacteria that can cause rare, serious infections in a bite or an open wound.
• People with weakened immune systems are at higher risk and should talk to their doctor.

What lives in a dog's mouth

The 2012 study sequenced 5,958 bacterial DNA fragments from dogs' mouths and sorted them into 353 groups of bacteria, from 148 genera. About 80% of those groups had no formal name yet. When the researchers compared them with the bacteria in human mouths, the two communities were markedly different, which they read as a sign that each mammal species carries its own distinct oral microbiome.

That community isn't fixed. A 2024 study of 96 companion dogs found 19 bacterial species whose levels rose or fell with age, and diet and dental care can also change the mix. Our oral microbiome hub gathers our guides on what lives in a dog's mouth.

Why "cleaner" is the wrong question

A mouth is never clean in the sense of being free of bacteria. Every healthy mouth, canine or human, hosts a large community of microbes, and most of them do no harm where they belong. The useful comparison isn't which mouth has fewer bacteria, but which bacteria each one carries. For dogs and people, the answer is mostly different ones.

Dog licks and kisses: what to know

The U.S. Centers for Disease Control and Prevention notes that Capnocytophaga bacteria are commonly found in the mouths of dogs and cats. They can make people sick if they get into the body through a bite or through saliva in an open wound or sore. The CDC also points out that most people who have contact with dogs don't get sick, and that people with weakened immune systems are at higher risk.

• Keep licks away from cuts and sores, and wash any wound a dog has licked.
• Wash your hands after close contact, especially before you eat.
• After a bite, wash the area with soap and water right away and call a healthcare provider, as the CDC advises.
• If your immune system is weakened, for example during cancer treatment or without a spleen, ask your doctor how to stay safe around pets.

Keeping your dog's mouth healthy

Your dog's own oral health matters too. A 2019 study described periodontal disease as the most common oral disease of dogs, and the American Animal Hospital Association's dental guidelines stress that it can be prevented with regular dental exams and good home care. Our guide to a daily dental routine covers what you can do at home, and our guide to what causes bad breath in dogs explains when breath is worth a vet visit.

What a DNA kit's oral microbiome section shows

Some dog DNA kits now describe the bacteria in the saliva sample too. The PuppyGenes oral microbiome section is a snapshot of the bacteria measured in the sample, compared with a reference group; it does not diagnose or rule out dental disease. Our guide to what an oral microbiome test can and can't tell you explains how to read one.