Dog’s Mouths Are Not Cleaner Than Human’s

June 28, 2010 at 5:00 am 14 comments

This probably shouldn’t be a secret. If you think about the things that dogs lick and humans don’t, then this should be pretty obvious. But, the myth that dog’s mouths are cleaner than human’s is perpetually propagated.

There is an old tale that you should let a dog lick your wounds to speed healing. The wounds may actually heal faster; that’s because the licking will stimulate circulation and clear away dead tissue, but it’s not because their saliva is cleaner than ours.

Some say that dog’s saliva is more acidic than humans so they break down bacteria better. Others look at the fact that dogs rarely get cavities or gum disease as proof.

The fact is, dogs have a similar amount of oral bacteria to humans. But, the types of oral bacteria varies between dogs and humans.

That’s why dogs rarely get cavities or gum disease, the types of bacteria that cause these problems are only found in about 5% of dogs. In fact, viruses and bacteria that affect humans usually don’t bother dogs and vice versa. For that reason, you may actually have a higher risk of becoming sick from kissing a human than kissing a dog. But, that doesn’t mean their mouths are cleaner.

Broken Secrets | By: Chad Upton

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Sources: A Moment of Science, ABC, Life’s Little Mysteries

Entry filed under: Around The House, Demystified. Tags: , , , , , , , , , , , .

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14 Comments Add your own

  • 1. Nathan Wheeler  |  June 28, 2010 at 9:42 am

    How does this compare to the episode Mythbusters did where they took a culture sample from a dog’s mouth and a human mouth and the dog’s culture sample showed a significantly smaller bacteria sampling than the human culture sample? I do understand that there is still bacteria in the dog’s mouth, and this was reflected by the study.

    • 2. Chad Upton  |  June 28, 2010 at 10:05 pm

      I’ll have to watch the episode to comment on how it compares. It looks like they compared one dog to one person. I’d be interested to know what method they used to test for bacteria too. For those who are interested, here’s some info about that episode:

      • 3. Nathan Wheeler  |  July 1, 2010 at 10:37 am

        If I remember correctly, and it has been some time since I watched the episode, they used a sterile pad filled with nutrients (most likely agar) to “pick up” bacteria from objects, then placed them in a temperature controlled environment at a regular 98.6 degrees F. Then they visually checked for bacterial growth on the pads. Bacteria cultured like this will form into a colony large enough to be visible to the naked eye given enough time.

        I don’t remember for sure whether they compared more than one dog to more than one person or not, but I do remember that they for sure did the “toilet seat is cleaner than the rest of the bathroom” test in the same episode on multiple bathrooms and multiple areas of each bathroom.

  • 4. Max  |  June 28, 2010 at 12:47 pm

    You wrote “… you may actually have a higher risk of becoming sick from kissing a human than kissing a dog. But, that doesn’t mean their mouths are cleaner….”
    —- I would argue that it means exactly that. The definition of ‘dirty’ & ‘clean’ varies with the context. But in this context, the statement “Dogs mouths are cleaner than peoples” is equivalent to “contact is less likely to result in disease”. I.e., what a reasonable person has in mind when using or hearing “Dogs mouths are cleaner than peoples” is the relative risk of contagious disease. That risk is less from dogs’ mouths than from peoples’ . Therefore dogs’ mouths are cleaner.
    —- “Cleaner” doesn’t mean germ-free.

    • 5. Chad Upton  |  June 28, 2010 at 9:53 pm

      Thanks for the comment. I disagree with you, I think cleaner does suggest fewer germs rather than a lower risk level of the germs that do exist. That’s how I understand the dictionary definition of “clean” too.

      That said, if you’re just thinking about cleanliness in terms of kissing dogs then I think you could be right in some cases (not all dogs and all people have equally dirty mouths of course).

  • 6. Ex Lit Prof  |  June 28, 2010 at 2:17 pm

    My superiority complex vis-a-vis dogs has been completely shattered!

  • 7. Ana Pires  |  June 28, 2010 at 7:28 pm

    What Max says up there makes sense…

    But regardless, I love doggy and kitty kisses. :3

  • 8. Melissa  |  June 30, 2010 at 8:16 am

    Gum disease in dogs occurs just about the opposite of rarely. I don’t have any statistics for you, but I was a vet tech for a while and I can tell you that by the age of three or four, most dogs need to have their teeth cleaned–and that’s not just the company line, I assure you. Some breeds are worse than others, like dachshunds or miniature poodles. Dogs are programmed to hide disease, so you may never realize their teeth are in such bad condition until you physically check their mouths. I’ve heard more times than I can count, “But we never cleaned Buster’s teeth and he lived to be 18!” My question to that is whether or not Buster had any teeth left when he was 18. Just as the bacteria are similar in dogs’ mouths as in ours, if we never brushed our teeth, you can bet they’d get pretty nasty after a year or two.

  • 9. Ruby  |  January 9, 2012 at 2:45 am

    Regardless of whether or not a dog’s mouth is “cleaner” or not, I would rather not have an animal’s tongue all over me that is used as both his wash cloth and toilet paper. Seriously, if they are so clean and germ-free, they would not transmit rabies or other things that pose a threat to humans. If you want to kiss dogs, go for it. I would rather not kiss something that eats it’s feces and the food it spit back up partially digested. That goes for animals and people alike!

    • 10. chriscp  |  September 24, 2013 at 2:05 pm

      I mostly agree with you. I’ve never been the kind of person who kisses dogs on the mouth or lets them give my face a tongue bath. However, using the “transmit rabies or other things…” as the reason is flawed. Look at how many diseases we transmit to each other via mouth contact. That cold sore? Virus. Flu? Virus. In many cases, the other person’s mouth doesn’t even have to touch you. Sneezing gets the cooties across just fine.

  • […] mouth. I suppose you could take a sample of each and see bacteria growth rate over time. However, this article on suggests that the bacteria that occupies a dog’s mouth is different than that of which […]

  • 13. Siyad  |  December 27, 2012 at 11:02 pm

    There are 12 signs that dogs have in common with believer (mu’min) having cleaner mouth is one of those signs

  • 14. chriscp  |  September 24, 2013 at 2:01 pm

    I wouldn’t get all superior about the things dogs lick. Some people lick the exact same things; they’re just licking them on other people. ;)


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