Perhaps it's because we see dogs and cats doing it all the time. Maybe it's because we see friends put their contact lenses in their mouths to clean them. Or maybe it just seems natural that saliva should be considered clean, with healing powers all its own.
The fact is, as natural as it may be for animals to lick their wounds, the human mouth, as well as those of other animals, is full of bacteria. As a result, whatever healing capacity saliva may have, there is a real risk of infection that more than outweighs any benefits.
The Organisms in Your Mouth
Certain parts of the body are sterile, meaning that, under normal conditions, there are no bacteria or other organisms living there. For example, the urinary system, including the kidneys and bladder, should have no bacteria present. In fact, the finding of bacteria in the urine is usually a sign of an infection, including urinary-tract infections, or a kidney infection such as pyelonephritis. As odd as it may seem, your mouth is teeming with microbes, even soon after brushing your teeth or using mouthwash. It's simply a function of our anatomy and how we have evolved to coexist with these organisms; in fact, they may even help fend off infection with other less "friendly" infectious microbes.
The Problems With Mouth Bacteria
Most of the time, we never know we are harboring millions of bacteria in our mouths, but they can cause trouble, especially when their numbers or locations become unusual. Common examples include:
There is often a reason these problems arise; for example, poor dental care can make an infection around a tooth more likely.
Another problem related to bacteria in the mouth may be among the most underappreciated: human bites. When one person bites another, the injury may not be limited to the cut in the skin. These same bacteria living peacefully in the mouth of the biter easily can cause a serious infection in the bitten person's wound. The severity and rapidity of the infection is easy to underestimate. Fortunately, prompt treatment with antibiotics brings most infections related to human bites under control quickly. Similar problems can follow any contact with the human mouth that breaks the skin. For example, in a fistfight, the person who strikes the mouth of the opponent may wind up worse off if bacteria from the opponent's mouth causes a hand infection.
Animal bites also are prone to causing infection, although the types of bacteria vary depending on the species. As much as we may all worry about rabies related to animal bites, bacterial infections are much more common. Even playing with your pet can lead to a wound infection if its teeth break your skin.
The Bottom Line
Try as you may, your mouth will harbor bacteria, so worrying about them or trying to eradicate them is not useful under most circumstances. Even the best mouthwashes touting antibacterial effects only reduce their numbers temporarily. However, good oral hygiene (including regular brushing and flossing) and recognizing the risks of bites are important ways you can avoid the problems associated with oral bacteria. As for licking your wounds as a way to promote healing, some things are best left to the dogs. For us, soap and water are a better bet.
Robert H. Shmerling, M.D., is associate physician at Beth Israel Deaconess Medical Center and associate professor at Harvard Medical School. He has been a practicing rheumatologist for over 20 years at Beth Israel Deaconess Medical Center. He is an active teacher in the Internal Medicine Residency Program, serving as the Robinson Firm Chief. He is also a teacher in the Rheumatology Fellowship Program.