You have probably heard someone say it at least once. A friend lets their dog lick their face and casually mentions that a dog’s mouth is cleaner than a human’s. It sounds oddly believable, but is there any real science behind it? The short answer is no. This popular belief is a myth, and research gives us a clear picture of why.
This article breaks down the facts about dog and human oral bacteria, what risks dog saliva actually carries, and how to keep your dog’s mouth as healthy as possible.
The Myth: Where Did It Come From?
The idea that dog mouths are cleaner likely started from one simple observation. Dogs often lick their wounds, and those wounds sometimes heal quickly. People assumed the saliva must have some powerful cleaning ability.
Dog saliva does contain enzymes like lysozyme and peroxidase, which can help reduce certain bacteria. However, that does not mean the mouth itself is clean or free from harmful germs. The myth likely stems from the fact that dogs sometimes lick their wounds and heal without any infection, but that does not mean they have cleaner mouths.
Dog Mouth vs Human Mouth: The Bacteria Count
One of the most common pieces of evidence used to support the “cleaner mouth” claim is bacteria count. Here is what the research actually shows:
| Feature | Dog Mouth | Human Mouth |
| Types of bacteria | Around 600 to 714 species | Around 615 to 700 species |
| Common disease bacteria | Porphyromonas gulae | Porphyromonas gingivalis |
| Periodontal disease risk | Very high (80% of dogs by age 2) | Lower with regular dental care |
| Zoonotic bacteria present | Yes (Capnocytophaga, Pasteurella) | Less cross-species risk |
| Dental hygiene frequency | Rarely done at home | Usually daily brushing and flossing |
One recent paper found that dogs had 714 types of bacteria in their mouth, while the National Institutes of Health says human mouths contain around 700 types. Many of these microorganisms are unique to either dogs or humans.
So the numbers are very similar. The key difference is not how many bacteria exist, but which ones and how dangerous they can be to the other species.
Are Dog and Human Mouth Bacteria the Same?
No, they are mostly different. Humans have bacteria like Streptococcus mutans and Porphyromonas gingivalis, which contribute to cavities and gum disease. Dogs have a different microbial makeup, including Porphyromonas gulae, which is linked to periodontal disease in canines.
Many of the bacteria in a dog’s mouth are species specific, so they will not necessarily harm the dog’s owner. This is actually where the myth gains a tiny bit of ground. Because most dog bacteria do not transfer well to humans, casual contact usually causes no harm.
However, some bacteria do cross the species barrier and that is where things get risky.
Bacteria in Dog Saliva That Can Harm Humans
While the risk is low for healthy adults, dog saliva is not completely harmless. Here are the main bacteria to know about:
Capnocytophaga canimorsus
Capnocytophaga canimorsus is a bacterium commonly found in dog saliva that can be dangerous to humans if it comes into contact with a minor wound, such as from a dog licking it. While rare, there have been documented cases of people developing septicemia from it.
Pasteurella canis
Pasteurella canis is the most common bacteria found in a dog’s mouth and is also the most common organism found in a person who has been bitten by a dog.
Rabies virus
Rabies is a very serious infection that dogs can pass through their saliva. If a dog has been infected with the rabies virus, it works its way through the nervous system and eventually to the brain.
Salmonella and E. coli
If your dog consumes Salmonella or E. coli contaminated food, these pathogens may be transmitted to you if your dog’s slobber enters your mouth. Although a raw food diet is more susceptible to contamination, any dog food can become contaminated.
Who Is Most at Risk from Dog Saliva?
People with weakened immune systems, young children, older adults, and anyone with cuts are at higher risk of illness from dog saliva.
For most healthy adults, a dog licking your hand or face poses very little real danger. The risk increases significantly when:
- The dog licks an open wound
- Saliva enters your eyes, nose, or mouth
- You have a compromised immune system
- The dog has not been vaccinated or receives no veterinary care
Why Dog Mouths Tend to Be Less Hygienic in Practice
Even setting bacteria aside, dogs simply use their mouths in ways that introduce far more contaminants than humans do.
Dogs use their mouths to explore their environment, increasing their exposure to pathogens humans do not typically encounter. Think about what a dog does with its mouth on any given day:
- Chewing on outdoor sticks, shoes, or dirty toys
- Licking their own body including private areas
- Eating food off the ground
- Sniffing and sometimes eating waste from other animals
- Drinking from puddles or standing water
Humans, on the other hand, generally limit what goes in their mouths and practice oral hygiene daily.
Periodontal Disease: Dogs Are Far More Affected
By the time dogs are 2 years old, around 80 percent of them have periodontal disease, a condition associated with bacterial infections.
This is largely because most dogs never have their teeth brushed. Without consistent dental care, plaque and tartar build up rapidly, leading to gum disease, bad breath, tooth loss, and even infections that spread to the heart and kidneys.
Humans, with regular brushing, flossing, and professional cleanings, have far better oral health outcomes on average. This alone makes the “cleaner mouth” claim difficult to support.
How to Keep Your Dog’s Mouth Clean
Good dental hygiene for your dog is simple once you build a routine. Here are practical steps you can follow:
- Brush their teeth daily using a dog safe toothbrush and dog toothpaste. Never use human toothpaste as xylitol in it is toxic to dogs.
- Offer dental chews like Greenies or other vet recommended treats that reduce plaque buildup naturally.
- Use water additives that are designed to reduce oral bacteria and freshen breath.
- Provide chew toys with ridges or bristles that help clean teeth during play.
- Schedule annual vet dental cleanings to catch and treat any early signs of gum disease.
Is It Safe to Let Your Dog Lick Your Face?
For most healthy adults, letting your dog lick your face carries minimal risk. Because your skin absorbs saliva poorly, a dog licking your skin poses little risk of infection as long as they are not licking a wound.
That said, it is a good idea to avoid letting dogs lick your mouth directly, especially if you are pregnant, elderly, have young children, or have any cuts or sores on your skin.
Frequently Asked Questions
Is a dog’s mouth actually cleaner than a human’s?
No. Both dogs and humans have around 600 to 700 types of oral bacteria, and a dog’s daily habits expose its mouth to far more contaminants than a human’s.
Can I get sick from my dog licking me?
The risk is very low for healthy adults. Risk increases if the dog licks an open wound or saliva enters your eyes, nose, or mouth.
Why do dogs lick wounds and does it help?
Dogs lick wounds by instinct. While saliva has some mild antibacterial enzymes, excessive licking can slow healing and introduce harmful bacteria like Pasteurella into the wound.
What bacteria in dog saliva is most dangerous to humans?
Capnocytophaga canimorsus and Pasteurella canis are the most commonly noted bacteria that can cause infections in humans, particularly through dog bites or contact with open wounds.
How can I improve my dog’s oral health?
Brush your dog’s teeth daily with dog safe toothpaste, offer dental chews, use water additives, and schedule annual professional dental cleanings with your vet.
Conclusion
The idea that a dog’s mouth is cleaner than a human’s is simply not supported by science. Both species carry hundreds of types of oral bacteria, and the overall numbers are surprisingly similar. What differs is the type of bacteria, the hygiene habits, and the behaviors that expose each mouth to outside pathogens.
Dogs have unique bacteria that are mostly harmless to humans under normal conditions. But their habits, lack of regular dental care, and exposure to environmental contaminants make their mouths far from clean in any practical sense. Enjoy your dog’s affection, keep up with their dental health, and wash your hands or face after those slobbery kisses.