Buzz
Comparing a dog's mouth to a human's is like comparing two very dirty fruits—apples and oranges. Both species have mouths that are warm, moist, and home to almost identical amounts of bacteria. Neither can be considered clean, and any debate about their relative cleanliness is moot because the majority of the bacteria is species-specific. The germs in your dog's mouth won't pose much of a risk during a slobbery kiss. In fact, you're more likely to get sick from kissing another person than your dog, as bacteria from a human's mouth will feel just as comfortable in yours.
That said, not all bacteria are species-specific. Dogs and humans can share some germs through their mouths, so if your dog is a face-licker (are there any that aren't?), there are a few steps you can take. First, prevent your dog from picking up harmful bacteria by keeping them away from the trash (and spoiled food), and out of contact with wild animals (to avoid diseases like rabies). Second, keep your dog healthy with regular vaccinations, parasite control, and teeth brushing.
Now, pucker up!
While we're on the subject, let's address two common beliefs about dogs: 1) Dogs lick their wounds and heal quickly, and 2) Dogs are less prone to cavities than humans. Both have simple explanations. Licking wounds helps remove dead cells and dirt, much like when we clean our own injuries. From there, the immune system takes over.
As for cavities, they are mostly caused by the bacteria Streptococcus mutans, which thrive on sugar. Since sugar is much more prevalent in a human's diet than a dog's, S. mutans prefers to reside in our mouths rather than in Fido's.
[This Big Question originally appeared in 2010.]
