Are Dog Mouths Cleaner Than Human Mouths?

You've probably heard (or even said) this excuse anytime a friend shares a kiss on the mouth with their canine companion: "their mouths are cleaner than ours! I read it… somewhere." While it's true that dog saliva does contain some antibacterial properties, the rumor that a dog's mouth is cleaner than a human's mouth is just that — a rumor. But, is that even true? And, why do so many people assume it that it is?

An adorable Parson Russell Terrier looking happy at the camera
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Are dog’s mouths clean?

While the answer to this question will, of course, depend on the dog, the objective answer to this question is yes, for the most part. Dogs, like humans and every other mammal on earth, have certain healthy bacteria that live on their skin and in their mouths at all time, which are necessary for maintaining proper working function. If a healthy dog's saliva comes into contact with a healthy person's skin, or even mouth, it is generally unlikely that that person will fall ill. However, if your dog is the type to enjoy a mouthful of fecal matter, eat a decaying animal, or just engage in otherwise objectively disgusting pursuits, the healthy bacteria in her mouth won't magically sanitize any of those things away.

All that being said, there can be unhygienic complications that come about as the result of a dog kiss. According to The Conversation, one such bacteria found in the mouths of dogs and cats is called Capnocytophaga canimorsus. Up to 75% of dogs in good health are said to live with this bacteria in their mouths, which doesn't generally pose a threat to them, and in many cases, won't harm humans who come in contact with it either. Sometimes, however, people with weakened immune systems, like the elderly, and young babies, can become negatively affected by a dog's saliva, and can sometimes even experience sepsis as a result of complications from being exposed to the bacteria. Additionally, rabies, toxocara canis, and salmonella are all diseases that can be contracted from a dog's saliva.

small dog licking woman's nose
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Why dogs lick wounds

The belief that a dog's mouth is cleaner than a human's likely stems from the fact that dogs lick their own wounds in an effort to heal. According to a study conducted by the School of Veterinary Medicine at UC Davis, dog saliva was found to be capable of fighting certain types of bacteria, namely. E. coli, and Streptococcus canis. This is why dogs instinctively lick their wounds — to prevent these bacteria from infecting the sore should they come into contact. Additionally, this licking behavior works to keep young puppies not only clean, but potentially free from diseases associated with these bacteria. Mother canines will often lick her own mammary glands, as well as the genital organs on both herself and her litter as a way to prevent the spread of E. coli and strep among her babies, who are highly susceptible to contracting diseases at such a young and vulnerable time in their lives.

So, a dog can lick her own wounds to keep herself safe from possible diseases, and will offer than same service to her young puppies, but does that mean your dog's bacteria can heal your wounds? Technically, it could, but you still shouldn't let your dog do it. According to a report published in Psychology Today, proteins called histatins, and Nerve Growth Factor, both of which are found in saliva, have been shown to increase healing and encourage cell regrowth in the skin, thereby helping close an open wound. Additionally, nitric oxide is created when saliva contacts skin, which can protect cuts from becoming infected by bacteria. Because there are a number of other bacteria found in a dog's mouth, however, poses too much of a risk to expose an open wound to, even with helpful agents like these ideally working to heal the skin.

In addition to contracting a possible disease to a dog through sharing a kiss, we can pass potentially harmful things onto them. Zoonotic diseases and drug-resistant strains of bacteria have been passed from people to their dogs, which can lead to increased risk of infection for them. If you must kiss your dog, it's probably better left on the top of the head, and if they lick you to show their affection, be sure to keep it in an area where the skin is closed.

Shar-pei puppy dog licking his paw
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Keeping your dog’s mouth clean

If you're going to share a smooch with your dog, or even let her lick your skin or face, there are some things you can do to possibly prevent the spread of harmful bacteria, and just keep generally healthy hygienic practices. First, if you have a weakened immune system, it's best to err on the side of caution and resist the urge to engage in a dog kiss, no matter how clean you belief your canine's mouth to be. Additionally, your dog's diet can contribute to the overall oral hygiene of your pet, and can prevent the formation of harmful dental disorders like plaque, which can contribute to the accumulation of bacteria, says Merck Veterinary Manual. For food, snacks, additives, and other products designed with your dog's oral hygiene in mind, visit the Veterinary Oral Health Council for a list of approved products.

Brushing your dog's teeth can also make a big impact on keeping bad bacteria at bay, while simultaneously preventing possible periodontal diseases in dog's, like gingivitis. VCA Hospitals recommends brushing your dog's teeth twice daily, although any brushing is better than no brushing at all. When brushing, be sure to use a toothbrush and toothpaste created for a dog's mouth and system, as some toothpastes, like baking soda varieties, can contain alkaline material that can disrupt the acid balance in your dog's digestive system. Finally, be sure to wash your hands thoroughly with antibacterial soap and water after handling your dog's mouth to prevent the spread of possibly harmful bacteria, and rinse your dog's toothbrush well after use.