Coronavirus disease is spread by direct and indirect routes.
Direct transmission occurs after virus particles in microscopic respiratory droplets are expelled into the air, such as when an infected person coughs or sneezes, talks or breathes. Indirect routes include touching contaminated surfaces followed by your face, which is why hand washing is so vital.
Some people worry about indirect transmission by another potential route: via sweat, which would make the fluid ‘infectious sweat’. If such a thing existed, it would create risk at gyms and other sports centres as exercise should lead to sweating, and infectious sweat could contaminate shared equipment.
Can sweat spread Covid-19? That question is also a concern for people with ‘hyperhidrosis’ — a condition that causes extreme, uncontrollable sweating. And according to the International Hyperhidrosis Society, sweat “could actually help prevent the transmission of Covid-19.” The organisation supports that claim with quotes from experts like dermatologist Adam Friedman of the George Washington University, who notes that “Sweat has some inherent antimicrobial activity.”
But while that may sound like a definite answer, argument from authority is not scientific evidence — you have to read the research and point to papers. So what does science actually say about a link between sweat and coronaviruses?
The most highly-cited paper to mention a possible connection is a 2004 study led by pathologist Yanqing Ding at the First Military Medical University in Guangzhou, China, and virologist Shibo Jiang from the New York Blood Center.
The Chinese scientists surveyed the distribution of the original SARS-CoV-1 virus across different organs of dead patients and detected the pathogen in the sweat glands, stating that it “may be excreted […] via sweat, thereby leading to virus transmission.” Essentially, SARS-CoV-1 could escape through skin cells.
Finding a parasite in unexpected tissues doesn’t necessarily mean they normally use that route to spread from host to host, however, and the study didn’t offer evidence of excretion via sweat, it was just a proposed route of transmission.
Recently, psychologist Ruth Propper of Montclair State University in New Jersey wrote a commentary article in which she suggested that one possible route of transmission may be via “infectious sweat.” Propper argued that sweat could contain SARS-CoV-2 as its relative SARS-CoV-1 was detected in sweat glands (the 2004 study) and because “other lethal viruses may be contagious via sweat.”
The “other lethal” virus turns out to be Ebola, which has some similarities when compared to coronaviruses, but also many differences. Most notably, Ebola Virus Disease has been proven to spread via direct contact with bodily fluids of patients with symptoms, whereas Covid-19 is airborne and primarily transmitted via respiratory droplets — sometimes by asymptomatic carriers.
Propper’s article is scattered with spurious links and idle speculation, and should have been rejected by a biologist during peer review. Nonetheless, we can’t yet completely rule-out the possibility that Coronavirus is shed then absorbed via the skin.
Sweating can help spread Covid-19. That’s not because virus-laden ‘infectious sweat’ might drip onto surfaces, but because sweating will bring your hands into contact with the droplets released from your respiratory tract — and if you’re uninfected, that region is also where a coronavirus can gain entry to your body.
Simply put, Coronavirus is spread indirectly as a consequence of sweating. When you wipe the sweat from your brow during physical activity such as exercise or manual labour, you touch the area where respiratory droplets are most commonly found, a ‘T-zone’ around your eyes and nose, mouth and chin.
You might transfer virus particles from your face to an object like a door handle or free weights. Unless they’re cleaned with disinfectant, another person might then touch those contaminated surfaces and infect themselves after touching their own face.
Touching your face is hard to consciously control and happens without you even realising. A 2020 review by epidemiologists at the University of Auckland in New Zealand revealed that face-touching happens far more often than you might think: on average, people touch the T-zone almost 69 times per hour.
The implications of frequent face-touching during sweaty activities such as exercise are clear: you should be extra careful and get into habits like taking your own towel and sweatbands to the gym.