Could Repeated Face Touching Confer Evolutionary Protection Against Infection?

Touching one’s face can heighten infection risk, but it may also help protect the body by fostering microbial diversity, according to a recent study.

Humans touch their faces anywhere between 9.5 and 162 times per hour, according to previous research, a behavior that amassed heightened importance as the world raced to stop the COVID-19 pandemic.

Touching one’s face is a good way to spread germs, so in the pandemic, public health officials urged people to limit face-touching, wear masks to shield their faces, and frequently wash and sanitize their hands.

Yet, in a new article in the journal The Ocular Surface, corresponding author Minas T. Coroneo, MS, MD, and colleagues posit a more complicated hypothesis: that while carries with it significant risks, it can also bring benefits.

Coroneo, of the University of New South Wales, in Australia, and colleagues began by outlining the risks associated with spontaneous face touches, which extend far beyond spreading SARS-CoV-2, which causes COVID-19. Viruses like the herpes simplex virus and the human papillomavirus can infect the ocular surface, leading to ocular consequences. Herpes simplex virus, they noted, is the leading cause of infectious corneal blindness in the developed world.

Frequently touching one’s face and eyes can lead to infections in other parts of the body, too, they noted.

“Clearly, [spontaneous face touches] SFT plays an important role in respiratory disease, as hand-washing alone can reduce the risk of respiratory infection by 6–44%,” they said, explaining that angiotensin converting enzyme-2 (ACE-2) receptors, which are susceptible to infection by SARS-CoV-2, are found in the conjunctiva, cornea, nasal, and oral mucosa.

“Through tear film conveyance via the nasolacrimal duct, ocular surface pathogens have access to the nasopharynx, oropharynx, and the respiratory and gastrointestinal systems beyond,” Coroneo and colleagues added.

Still, the authors wrote that the high rate at which humans touch their faces, and the absent-minded way in which they do it, suggests it may have an evolutionary benefit.

One possible benefit, they said, may come from the bacterial diversity present on the surface of human hands.

“While SFT has previously been hypothesised as the cause of colonisation of healthcare workers with S aureus, we hypothesise that SFT may be important, or perhaps even essential, in developing and maintaining the diversity of the human microbiome,” Coroneo and colleagues wrote.

The investigators noted that the hands touch a wide variety of surfaces, and thus are exposed to a wide variety of bacteria. The hands also touch surfaces with mucus membranes, as well as the mouth and nose, implicating the respiratory and gastrointestinal tracts.

“Diversity is integral in maintaining microbiota homeostasis, with self-touch potentially serving as a pathway to increasing diversity in the microbiome of the ocular surface, skin, gastrointestinal and respiratory tracts, as supported by the high percentage of touches involving mucous membranes,” they wrote.

This could mean, they posited, that by fostering microbiota homeostasis, SFT actually ends up making humans more resistant to infection.

“Perhaps the commensal microbial immunity benefit of SFT has, from an evolutionary perspective, balanced against its significant infective risk,” they wrote.

Coroneo and colleagues closed, however, by returning to the current pandemic, noting that even if SFT has evolutionary benefits, it can also be dangerous in the current moment. They noted that face masks do not provide direct protection to the eyes, though they said some evidence suggests when people wear a mask they decrease their overall rate of spontaneous face touches. Thus, this habit remains a significant public health concern amid the pandemic, they said. From a longer perspective, though, the issue is more complex, they said.

“Whilst SFT may be important in mutualistic microbiota exposure, this also increases the risk of pathogen exposure,” Coroneo and colleagues concluded.

Reference

Spencer SKR, Francis IC, Coroneo MT. Spontaneous face- and eye-touching: Infection risk versus potential microbiome gain. Ocul Surf. Published online April 30, 2021. doi:10.1016/j.jtos.2021.04.008