The saying “licking one's wounds” is a metaphor that is synonymous with withdrawing and recovering from a wound, and behavior is observed in some pets and other animals. Dogs do it; Mice do it; even ants do it. All kinds of bugs apply their saliva to scratches and scratches. But why do these animals lick their wounds?
The answer lies largely in the self-soothing actions of licking and the healing properties of saliva. Licking wounds is an instinctive response, perfected by natural selection, that can relieve irritation and pain and even help injuries recover faster, according to Dr. bBenjamin Hart, a retired veterinarian and professor emeritus at the University of California, Davis.
But in dogs and other pets, instinct can easily backfire, especially when better wound treatments are available.
For animals “without thumbs or medicine,” licking is “the best they probably have,” said Dr. Kristi Flynn, a veterinarian and animal behavior expert at the University of Minnesota. Licking can remove debris, such as dirt or pieces of loose skin, from a wound, while helping to relieve pain, according to Flynn. It is similar to how a person might rub their foot after hitting a toe or grabbing their arm after leaning against a hot stove. “When animals are in pain, it's a natural inclination to try to calm an area,” Flynn explained.
Hart agreed. “Licking wounds is an instinct in dogs that goes back to the wolf's ancestor,” he remarked. “They have a wound; they have an instinct to lick it: keep it clean and wash away dirt and grime.” And beyond the immediate attempt to calm down, research by Hart and others has shown that the saliva of some animals (including humans) has antibacterial and growth-promoting properties of tissues and nerves that accelerate healing.
For example, dog saliva is effective in killing Streptococcus canis, a form of streptococcus that primarily infects animals, and E. coli bacteria,b according to a 1990 study co-written by Hart and published in the journal Physiology & Behavior . Another 2018 study comparing canine and human saliva from the journal PLOS One found multiple immune and cell growth proteins specific to dog saliva.
Meanwhile, rodent saliva contains compounds that promote skin growth and wound closure, according to a 1979 study in the journal Nature and a 1991 study in the journal Experimental Gerontology. Similar growth factors are also found in small amounts in human saliva, according to a 2019 study in the Archives of Oral Biology .
However, in the age of modern medicine, for both pets and people, licking wounds can cause more harm than good, which is why cats and dogs often return home from the vet with a plastic collar.
Licking the site of a surgical wound can damage or pull out the sutures, and this “causes a very small injury to become a big disaster,” Flynn said. Dogs are especially prone to over-licking themselves, which can prevent injuries from healing. “They make a mountain out of a grain of sand and they just don't have the judgment to stop,” he said.
“Licking wounds can also increase the risk of infection by introducing oral bacteria into the injured site,” the expert added. Although saliva has some antibacterial properties, it is not a universal germ killer. For example, Hart's 1990 research revealed that canine saliva did not kill Staphylococcus, a genus of bacteria that cause staph infections and are commonly found in wounds.
So if licking one's wounds is not particularly beneficial, why did it evolve and persist for many generations? “Things that evolve are not 100% correct,” Hart remarked. “They have to be useful 75% of the time or 50% of the time, and yet they will be maintained by natural selection because it is better than nothing.”
But modern science and medicine tend to advance faster than evolution. Licking wounds is a good solution for wild animals that have no other alternatives. However, for owners of cats and dogs, it is better to listen to the advice of a veterinarian.
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