Every other Friday, the Outside/In team here at NHPR answers listener questions about the natural world.
“I am wondering why animals lick their wounds. . . . I see my dog do it, but I don't think humans should. I wonder if animals have something different that makes licking their wounds good for them, or if it's actually just bad for them, or if there's some other story here,” asked Luke, calling from Richmond, Virginia.
To submit a question to the Outside/In team, you can record it as a voice memo on your smartphone and send it to outsidein@nhpr.org. You can also leave a message on our hotline, 1-844-GO-OTTER. No question is too serious or too silly.
This transcript has been lightly edited for clarity.
Justine Paradis: Wound licking is thought to be instinctual. Not only do dogs lick their wounds, but so do cats, rodents, bison, and primates — including humans.
Henk Brand: It’s not only animals doing this. If you in the morning are preparing your sandwiches for lunch and you accidentally cut your finger. . . . You put your finger in your mouth.
Justine Paradis: That’s Henk Brand, a medical biologist at the Academic Center of Dentistry in Amsterdam. When animals lick a wound, their tongue is physically cleaning it by removing debris and dead tissue. But there’s also a chemical agent involved: saliva, which is the focus of Henk’s research.
Humans actually have plenty of old legends about saliva, from the Scottish Highlands to ancient Rome. There's an old French folk saying which translates to “the best doctor is the mouth of the dog.” And it turns out these legends are kinda right. Saliva isn’t just for digestion.
Henk Brand: 99% of saliva is indeed water. However, the other 1% . . . are the very interesting part.
Jane Sykes: There's a bunch of different proteins and growth factors in saliva that might help with like blood clotting and wound healing. Saliva even contains analgesic substances that might help to reduce pain.
Justine Paradis: This is Jane Sykes, a professor of veterinary medicine at UC Davis.
Jane Sykes: When you actually think about wounds in the mouth — an ulcer, or you lose a tooth — the wounds often heal much faster than wounds on the skin, possibly because of the effect of all of these substances in saliva.
Justine Paradis: This is a little puzzling, because another thing about the mouth is that it is a perfect environment for bacteria. If oral bacteria does find its way into an open wound, it can be very dangerous. There’s this one case study about an immunocompromised individual licking their finger after hurting it in a bike accident, resulting in infection and, eventually, a partial amputation of the thumb.
If a dog were to lick that same open cut on a human hand, the risks of a serious infection might be even greater, especially for babies or immunocompromised people. So, turns out the best doctor actually isn’t the mouth of the dog. But as for a dog licking its own wound?
Jane Sykes: Interestingly, unless a bite wound is involved . . . we often don't see these particular bugs causing infections in dogs and cats that are just licking their own wounds. They more commonly get infections from growth of bacteria that normally live on the surrounding skin, rather than those that live in the mouth.
Justine Paradis: Still, wound licking can become obsessive and prevent healing. Jane recommends stopping pets from overdoing it, especially if it’s a surgical wound. You can use tools like the Elizabethan collar — more commonly known as the “cone of shame.”
Meanwhile, researchers like Henk think there’s a lot of therapeutic potential in the healing agents found in saliva.
Henk Brand: If you purify and synthesize them, you would have a kind of new generation of antibiotics.
Justine Paradis: In fact, his lab has already worked on reproducing one of these wound enhancing factors.
Henk Brand: We were able to synthesize it in the lab artificially, and it now is being added to some gels, etc. to enhance the wound healing effect of those gels.
Justine Paradis: But there are also other effective tools to care for open cuts, almost certainly in your house right now: soap and water. There are alternatives to licking our wounds.
