What if you're close enough to smell someone's secondhand smoke, or pass through a cloud of smoke on your way into a store? Does that expose you to the coronavirus, if the smoker happens to be infected?
There is little evidence to suggest the smoke itself could be carrying the coronavirus, but researchers and physicians say that merely being able to smell someone's cigarette is a warning sign you're breathing air that was just in someone else's lungs.
William Ristenpart, a professor of chemical engineering at the University of California at Davis who researches how pathogens are transported, told The Washington Post that the smoke particles themselves are unlikely to be carrying a virus that could infect other people. This is partly because the heat from the cigarette would probably kill the virus, but also because "a large fraction of the smoke particulates go into your lungs, never hit anything, and then are exhaled," Ristenpart said.
But there is reason to be concerned about transmission if you get a whiff of someone's smoke - the respiratory particles that come along with it.
"If you smell somebody else's exhaled cigarette smoke, then you are inhaling air that was in that person's lungs," Ristenpart said. "This means you could also be inhaling their virus-laden respiratory particles, which are composed of respiratory mucosa rather than ash."
Research is still inconclusive on whether the coronavirus can be transmitted in airborne particles, but the hypothesis is gaining traction. While the main source of transmission is believed to be large respiratory droplets - which do not hang around in the air for long before falling to the ground - some believe that certain outbreaks could have only been possible if the virus can be suspended in air.
A group of prominent scientists in July pointed to "superspreading" events, during which an infectious person unwittingly spreads it to many others, as evidence shows the virus is being transmitted long distances through the air in far smaller and more numerous particles.
This has implications not just about what's wafting around in exhaled cigarette smoke but about the hazards of indoor settings as well. William Nazaroff, an environmental engineer from the University of California at Berkeley, believes the coronavirus can be airborne and suggests we should consider modifying indoor ventilation systems to filter or kill the virus.
"It has to do with the plume of what is emitted and the extent it can infringe on your breathing zone," Nazaroff told The Post's Ariana Eunjung Cha.
Smokers also need to remove their masks to take a puff. Being around people who aren't wearing masks is inherently a risk, but on top of that, smokers tend to exhale more forcefully, according to Herman Gatzambide, a pulmonary specialist in Orlando who was interviewed by WFLA. Someone who isn't smoking may only project respiratory particles six feet, but it could be more like 10 or 12 feet for someone who is smoking.
"Not only are they potentially spreading virus by not wearing a mask, they are blowing those droplets to the people around them to potentially get infected," Albert Rizzo, chief medical officer for the American Lung Association, told the Associated Press.
Ristenpart said smelling someone's cigarette smoke "serves as a proxy to warn you that, 'Hey, I might be breathing in that person's virus.'"
Smokers themselves are also at higher risk of severe illness from covid-19, according to the Centers for Disease Control and Prevention. Smoking increases the risk of illness because it impairs lung function and makes it more difficult for the body to respond to respiratory infection.
Recent studies have shown young adults who smoke, even if they don't have other underlying health conditions, are more susceptible to severe symptoms, intensive care admissions and even death.