Can Dogs Help Humans Heal?

Science looks at whether dog saliva has healing properties.

Posted Jun 07, 2011

I was recently in a park where a mother and a grandmother were sitting on the bench watching a child play. A Golden Retriever was resting beside them also watching the activity. Suddenly the child slipped and fell down in such a way that she scraped her knee and caused it to bleed. The little girl ran over to her mother, who appeared to think that it was a minor wound. The family dog, however, stood up and began to lick the bleeding knee. This appeared to bother the mother much more than the wound itself, and she shooed the dog away with a look of disgust.

"Let the dog lick it," said the grandmother, "it will heal more quickly."

"That's a myth" insisted the mother. "It's much more likely that the dog's tongue will have contaminants from whatever he's been licking and that is much more likely to cause an infection then to cure it."

This got me to thinking about what the latest research is about the value of wound licking by dogs. Wound licking is an instinctive response in humans and many other animals to an injury. Dogs, cats, rodents, and primates all lick wounds. There is a common folk belief that animal saliva, especially that of dogs, has healing properties for human wounds. Evidence for this comes from a number of historical traditions. For example, in ancient Egypt, the city of Hardai became known as Cynopolis (City of Dogs) because, in its many temples dedicated to Anubis, the dog-headed guide of the dead, dogs were used as offerings.

However, dogs were also used in healing practices there since they strongly believed that being licked by a dog, especially in those areas of the body containing sores or lesions, would help to heal the injury or cure the disease causing it. This practice was picked up by the Greeks, and temples dedicated to Asclepius, their god of medicine and healing, often contained dogs trained to lick wounds. In the middle ages, Saint Roch was said to have been cured of a plague of sores through being licked by his dog. The value of being licked by a dog is still believed by many cultures to have curative powers. There is even a contemporary French saying, "Langue de chien, langue de médecin," which translates to, "A dog's tongue is a doctor's tongue."

The simple mechanical action of a dog's tongue can be helpful in dealing with a wound. The saliva of a dog's tongues acts to loosen any debris that may be on the surface of the wound. Any dirt or other debris will also become attached to the moisture of the saliva, thus at the very least, the area of the wound will be cleansed.

However, the focus of much research has been on the various antibiotic and helpful compounds that are found in a dog's saliva. The healing powers of saliva have long been suspected because lesions inside the mouth mend more quickly and scar less than wounds on the skin. Menno Oudhoff of the University of Amsterdam found simple proteins called histatins in saliva. These are well known for their ability to ward off infections. Some histatins also prompt cells from the skin's surface (called the epithelium) to close over a wound more quickly.  Oudhoff noted, "The first thing that needs to happen for wound healing is to activate the migration of epithelial cells."

Nigel Benjamin, a clinical pharmacologist with St. Bartholomew's Hospital and the London School of Medicine and Dentistry, claims that licking wounds is as beneficial to humans as it is to animals. His research showed that when saliva comes in contact with skin, nitrite—a natural component of saliva—breaks down into nitric oxide, a chemical compound that is effective in protecting cuts and scratches from bacterial infections. In addition, researchers at the University of Florida at Gainesville have discovered a protein called Nerve Growth Factor (NGF) in saliva. Wounds doused with NGF healed twice as fast as untreated (that is unlicked) wounds.

However, the data on wound licking is not all positive. In the mouths of mammals, we also find certain anaerobic bacteria such as Pasteurella. While not harmful in the mouth, Pasteurella can cause serious infections when introduced deep into an open wound. There are a number of reports of this happening, and sometimes the results have been extremely negative, causing infections that have resulted in amputations, and sometimes the resulting infections have been life-threatening.

One of the interesting aspects of these findings is the suggestion that the helpful chemicals are not only found in the saliva of dogs but also in the saliva of people. This suggests that if you are willing to ignore the possible complications to gain the healing benefits of having wounds licked, one may not need the assistance of Lassie or Fido. You can actually do it yourself. However, this does not mean that you should indiscriminately offer the benefits of your healing tongue to others.

You should be aware of the case of an Oregon teacher who was reprimanded after licking the blood from wounds on a track team member's knee, a football player's arm, and a high school student's hand. An Oregon public health officer commented, "We do know that animals lick their own wounds, and it may be that saliva has some healing properties. But my very strong recommendation is that you confine yourself to licking your own wounds."

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