While attending San Diego State College in the early seventies, my work-study job was in the vivarium, a room for keeping and raising animals for observation and research. We called it the animal room. I fed them and cleaned their enclosures daily, getting to know some of them intimately.

One behavior I learned from the primates was grooming, a behavior characterized by one individual manually or orally manipulating the hair or skin of another individual. While this behavior did serve a hygienic function, grooming is also well-known to facilitate and reflect social bonding between individuals.

After observing them groom each other, I began to engage in the practice with them, allowing them to groom me. It involved picking at scabs and flaky places on the skin and eating them. Years later, after one of my primate “friends” was transferred to the zoo, she would recognize and greet me.

And while we’ve been told not to pick our scabs, after injury to the skin it is instinctive for animals and man to lick the wound, promoting healing and reducing bacterial contamination. There have been reports that Fijian fishermen deliberately allow dogs to lick their wounds to promote rapid healing.

When Ann Wigmore, the founder of wheat grass therapy, had both of her ankles shattered in a horse and wagon accident as a child, her father gave his consent to have her feet amputated just above the ankles. Fortunately, she had just turned 18, and could reverse his decision.

Sunshine, eating grasses and the instinct of a little dog who licked her wounds, as well as her own determination to heal, eventually restored her feet to health and strength.

Saliva contains antimicrobial substances including thiocyanate which promotes bacteriostatic processes and lysozymes, spherical vesicles that contain around 50 enzymes that can digest many types of biomolecules, including proteins, DNA, RNA, polysaccharides, and lipids. Lysosomes are acidic and have a pH that’s optimal for the enzymes’ activity, similar to the stomach.

Furthermore, salivary glands concentrate nitrate which is rapidly converted to nitrite by facultative anaerobes on the tongue surface. When acidified, nitrite is converted to nitric oxide, a powerful antimicrobial substance manufactured by mammalian cells from L-arginine in response to invading microbial pathogens.

Since the surface of skin is acidic, it is postulated that salivary nitrite may, on contact with the skin, produce nitric oxide. To test this hypothesis testers measured nitric-oxide synthesis from the skin of 14 healthy volunteers’ hands after asking them to lick them all over and compared this with the effect of 0·9% saline solution.

The finding suggests that nitric oxide derived from salivary nitrite applied to the skin contributes to the antimicrobial effects of wound licking.