It seems as inevitable as cramped overhead space or a battle for the armrest: Someone on your flight is coughing, sneezing or sniffling. Or all three. And during flu season — not to mention a time when a fast-spreading new coronavirus has halted much of the world’s air traffic to and from China — that can be disconcerting.

So that’s it, right? Might as well call in sick as soon as you step into that confined, closely crammed space to hurtle through the air for a few hours?

It all depends, experts say. The biggest factor: whether your closest plane neighbors are sick.

The World Health Organization has said that passengers seated in the same row as well as two rows in front and behind of someone who is sick should be notified of potential exposure to infectious diseases. But a Boeing-funded study on transmission of respiratory diseases on planes published two years ago in the Proceedings of the National Academy of Sciences found that the danger zone is more narrow.

“It’s more of a one-row rule,” says Vicki Hertzberg, first author on the study and director of the Center for Nursing Data Science at Emory University. She said the people immediately in front of a sick passenger, two seats on either side or in the row in front or behind are the most vulnerable. The study applied to upper respiratory infections that could be spread through large droplet transmission.

“It’s not that you have to worry so much about the guy that’s four rows behind you that’s hacking,” says Hertzberg, a professor in Emory’s School of Nursing. “Maybe it’s just the person that’s immediately behind you or in front of you."

She said passengers in the aisle are at a higher risk of infection than those in a window seat because they are more exposed to potentially sick people as they pass by.

“So the strategy I take now for flying is, I take a window seat, and I don’t get up,” she says.

Passengers who end up near someone who is sick may have no good options, since planes so often fly full.

“You go to church and the person next to you is coughing, you move a row back,” says David Weber, a professor at the University of North Carolina School of Medicine and medical director of the infection-prevention department. “Can’t do that on a plane.”

While warning that anyone with a “known active communicable disease” should not fly, the World Health Organization also offers some reassurance to nervous air travelers.

“Research has shown that there is very little risk of any communicable disease being transmitted on board an aircraft,” the agency says, citing the high-efficiency particulate air filters that planes use on recirculated cabin air. If that ventilation system is not operating on the ground before takeoff, for example, contagious illnesses are more likely to spread.

The International Air Transport Association compares planes to other areas where people are close together for an extended period of time — though it notes that the air supply in plane cabins “is essentially sterile and particle-free."

“The overall risk of contracting a disease from an ill person onboard an airplane is similar to that in other confined areas with high occupant density, such as a bus, a subway, or movie theatre for a similar time of exposure … anywhere where a person is in close contact with others,” the group says. “That said, the risk on airplanes is probably lower than in many confined spaces, because modern airplanes have cabin-air-filtration systems equipped with HEPA filters.”

There are factors that can make people more prone to getting sick from flying, experts say. The air on planes is low in humidity, which can irritate mucosal membranes in the nose and mouth and skin, leading passengers to scratch and create tiny tears.

“If your nose has a little tiny microscopic gash in it, a tear, that’s a perfect place for a virus to land on and infect you,” says Howard Markel, a professor of the history of medicine and pediatrician at the University of Michigan.

And some viruses, influenza included, survive better in dry air, says Charles Gerba, a professor of microbiology at the University of Arizona. He has also tested tray tables on planes and found evidence of influenza, norovirus and methicillin-resistant Staphylococcus aureus, or MRSA. The latches on lavatory doors, he said, were also quite dirty.

“The moral of the story is, sit at a window, try to not go to use the toilet and don’t put the tray down,” Gerba says.

He and Weber both say they carry alcohol wipes when they fly to wipe down surfaces like armrests and tray tables. And while medical experts don’t agree on how well face masks work to ward off illness, Weber said he still carries one in case he cannot escape a sick seatmate.

“If everyone is coughing and hacking around me, I’ll put it on,” he says.

Hertzberg, the Emory professor, said one thing to leave off if people are coughing nearby is the overhead air vent. Rather than bathe a passenger with a clean flow of air, she says, it could actually help shoot not-so-clean air right at the person sitting underneath.

“It kind of attracts those droplets and then captures them into that airflow and pushes them down onto you,” she says.

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