According to the American Heritage Dictionary of the English Language, the phrase “to lick one’s wounds” means “to recuperate after a defeat.” Presumably this notion originated from observing animals licking their injuries after surviving an attack by a predator.
Of course, we modern humans do not need to resort to such instinctual practices given our access to antibiotics and sterile dressings. But is there any scientific evidence to suggest that wound licking can actually promote healing, in both animals and humans?
Evidence for the Health Claim
Dr. 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 human 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 unwanted bacteria. Benjamin also suggested that the nitric oxide could be used as a medication to block infection in the treatment of wounds as well as other skin conditions. Other research has shown that in addition to nitric oxide, human saliva contains other natural antibacterial agents—namely, lactoferrin and lactoperoxidase. Along with nitric oxide, these natural antibiotics could block the development of an infection, which is not only a serious threat to proper wound healing, but can also place the injured animal’s (and human’s) life at risk.
Evidence Against the Health Claim
Despite the antibacterial agents found in saliva, many scientists caution against wound licking, arguing that such practice is neither safe nor health-promoting. Human saliva contains a wide variety of bacteria that are usually harmless in the mouth but can cause significant infection if introduced deep within an open wound. It is well known that the bite of a human can often be more serious than the bite of an animal (assuming the animal is free of rabies).
A letter published in the April 2002 edition of the New England Journal of Medicine describes the case of doctors in Germany who were forced to amputate the thumb of a diabetic man who had licked a small wound caused after falling off his bicycle. The thumb had to be amputated after the wound became infected with flesh-eating bacteria. The man had fallen victim to a rare disease known as necrotizing fasciitis, which can destroy tissue in a little as 12-24 hours. Lab tests of the infected tissue showed the presence of two types of bacteria: Eikenella corrodens , commonly found inside the mouth, and Streptococcus anginosus , often found on the skin and in the throat. While this type of infection is extremely rare and, in this case, was probably worsened by the victim’s diabetes , applying human saliva to an open wound certainly has the potential to introduce numerous unsavory bacteria.
Once the bleeding stops, all efforts should be directed at preventing a wound from becoming infected. Animals in the wild have no recourse but to lick their wounds, presumably relying on the natural antibacterial properties of their saliva to promote healing. On the other hand, domesticated humans (and their pets for that matter), have an alternative–soap and water.
While there’s little harm in licking a paper cut to soothe the sting and draw away the blood, wound infections can be a serious risk in deeper cuts. Given the availability of highly effective preventive measures, the best use for your mouth would be to ask for help.