This article originally appeared in the San Francisco Chronicle’s health section on September 12, 2012.
Myth: Breathing recirculated air on airplanes increases your chances of getting sick.
Fact: You’re just as likely to catch a cold or other virus on a bus, in a classroom or in any other crowded place as you are on an airplane, researchers have concluded. It’s not the plane’s recirculated air you should worry about – it’s the person you’re sitting next to. If that passenger is ill, you may soon be, too.
Most commercial aircrafts recirculate 10 to 50 percent of the cabin air and mix it with fresh outside air. The recirculated air passes through sophisticated filters 20 to 30 times per hour, and according to the Centers for Disease Control and Prevention, the filters catch more than 99 percent of bacteria, fungi and viruses.
The air also circulates across the plane’s rows, rather than up and down the length of the plane, so passengers are mainly exposed to the air breathed by those sitting around them.
A 2002 study from UCSF monitored more than 1,000 passengers flying between the Bay Area and Denver. Some flew on Boeing 737s, which recirculate air, and others flew on Boeing 727s, which use 100 percent fresh air in the cabins.
In phone interviews five to seven days after the flights, 21 percent of passengers from the flights with fresh air reported having colds, compared with 19 percent of people on flights with recirculated air.
In 2005, authors of an article in the medical journal the Lancet concluded after examining several reports of disease transmission on airplanes that the risk of contracting many viral or bacterial illnesses on planes is greatest if you are sitting within two rows of a contagious person for more than eight hours. The risk of infection decreased exponentially to almost zero for passengers sitting 15 rows away.
Lancet researchers recommend the same preventive hygiene on airplanes that they recommend for everyday life: wash your hands with soap and water or use alcohol-based hand sanitizers, and try to avoid touching your mouth, eyes and nose during your flight.