The Maroons may be licking their wounds, but are there actually health benefits in doing it?

7 June 2018

While the Maroons are licking their wounds today after going down fighting in the State of Origin opener, spitting chips at some questionable refereeing decisions ("we was robbed!"), it’s timely to ask whether there are any healing benefits in licking actual injuries.

The healing benefits of saliva

By licking wounds we introduce saliva, and it turns out that the chemicals present might potentially help to promote healing. The idea that human saliva has wound-healing properties stems from the fact that oral mucosa, the mucous membrane lining the inside of the mouth, heals much faster than the skin. Saliva contains a cell-derived tissue factor – a protein necessary for the initiation of thrombin (which plays a vital role in the process of blood clotting). It also contains certain enzymes, such as lysozyme, cystatins, peroxidase and defensins, that are antibacterial in nature.

In a 2008 study, “Histatins are the major wound-closure stimulating factors in human saliva as identified in a cell culture assay”, Dutch researchers found that a small protein present in saliva called histatin, previously only believed to kill bacteria, was responsible for the healing of injuries and trauma-induced burns. 

"All skin wounds would benefit from licking." Dr Ole E. Sørensen

"We hope our finding is ultimately beneficial for people who suffer from non-healing wounds, such as foot ulcers and diabetic ulcers, as well as for treatment of trauma-induced wounds like burns," said Menno Oudhoff, first author of the report.

To come to this conclusion, the researchers used epithelial cells that line the inner cheek, and cultured in dishes until the surfaces were completely covered with cells. Then they made an artificial wound in the cell layer in each dish, by scratching a small piece of the cells away. In one dish, cells were bathed in an isotonic fluid without any additions. In the other dish, cells were bathed in human saliva.

After 16 hours the scientists noticed that the saliva treated "wound" was almost completely closed. In the dish with the untreated "wound," a substantial part of the "wound" was still open. This proved that human saliva contains a factor which accelerates wound closure of oral cells. Because saliva is a complex liquid with many components, the next step was to identify which component was responsible for wound healing. Using various techniques the researchers split the saliva into its individual components, tested each in their wound model, and finally determined that histatin was responsible.

The researchers believed that this is one possible explanation for why oral mucosa and wounds of the mouth (from teeth injuries) heal faster than wounds to bone and skin.

"It appears to be precisely the mucous in the saliva that stimulates white blood cells to form these effective nets of DNA and proteins," says author Dr Ole E. Sørensen, who runs an infection research lab at Sweden's Lund University. As a result, "all skin wounds would benefit from licking," Sørensen says, although big wounds with a lot of bleeding and tissue damage are probably not going to benefit, Sørensen says.

The Dutch study isn’t the only piece of scientific research demonstrating the wound healing capabilities of saliva. In a 2013 study “Saliva and wound healing”, a team of researchers found saliva plays a vital role in several cellular functions, including aiding in tissue regeneration and cellular movement. And in late 2015, Dr Sorensen conducted a study “A novel mechanism for NETosis provides antimicrobial defense at the oral mucosa” into the power of saliva by actually spitting on a series of samples. What he found was neutrophils, which comprise the majority of white blood cells and help combat infectious bacterial strains. To test the theory regarding neutrophils, Sorensen and his colleagues looked at people who didn’t produce saliva. These people had much higher rates of mouth infections and even ulcers due to the missing neutrophil cells.

Licking smaller wounds and injuries also debrides the wound and effectively decontaminates the specific region. 

"We don't know how much faster human wounds will heal with licking—and this will probably depend on the type of wound," he says. "However, it is known from rat experiments that a wound heals faster when licked."

Potential risks of licking wounds

Licking wounds may have some benefits that promote healing, but the practice also comes with a few risks. Although human saliva contains some compounds that aid in healing, the mouth is also home to a host of bacteria that are perfectly safe in the oral cavity, but may be dangerous if introduced into a deep wound through saliva. The principal risk of licking wounds is infection, especially in immunocompromised patients. 

The research helps answer the biological question of why animals lick their wounds - because they have no other recourse. We humans, however, are blessed with knowing how to use soap and water, disinfectants and antibiotics when required. While our immune systems have generally adapted to live in harmony with our oral and gut bacteria, letting a pet lick your wound is not only gross but also risky – just don’t do it.

So while the Maroons may be literally and metaphorically licking their own wounds today, they should always know to never lick a cane toad, and remember that all cockroaches are disgusting creatures that should only be stomped on, especially in Origin Two and Three. In most cases, the safest thing to do with youur mouth is to ask for help. Otherwise, just use a band-aid. And remember to chant “Queenslander!