This article originally appeared on Time.com.
When it comes to flying, nothing about a close proximity to strangers and bathrooms for hours on end feels particularly clean. And while you may not be able to make the flight shorter or the seats bigger, you can make your experience more sanitary by avoiding some of the dirtiest places on airplanes.
It’s worth noting that some people may be more susceptible to getting sick on planes because the cabin air humidity is under 20%, whereas home humidity is generally over 30%, according to the World Health Organization. The dry air exposure affects mucus, the immune system’s front line of defense, leaving people marginally more vulnerable to getting sick. A 2004 study in the Journal of Environmental Health Research found that people are far more likely — 113 times more, by one of the study’s measures — to catch the common cold during a flight than normal ground transmission.
Humidity aside, there are a handful of especially dirty spots, according to research and advisories from travel physicians. Here’s how to avoid them.
Airplane tray tables
The potentially grimiest place on an airplane unfolds right into your lap.
Alarmingly, a 2015 study by TravelMath that tested samples from hard surfaces in planes found that tray table surfaces had more than eight times the amount of bacteria per square inch than the lavatory flush buttons. The trays had 2,155 colony forming units of bacteria per square inch—compared to the 127 cfu/sq. in., which is what the National Science Foundation says is standard for a toilet seat at home.
Dr. Charles Gerba, microbiologist at the University of Arizona, tells TIME that the trays he’s tested through research have had cold viruses, human parainfluenza viruses, norovirus (which can cause diarrhea and vomiting) and the superbug MRSA, which causes skin infections.
The high amount of bacteria is likely linked to plane cleaning crews not having enough time between flights to wipe down the tray tables, the Wall Street Journal reports. And when they do get clean, those airlines may be using general cleaners instead of disinfectants.
In the meantime, to avoid eating dinner off a tray that someone piled used tissues or changed a baby’s diaper on just hours earlier, wipe it down with a sanitizing wipe, Dr. Michael Zimring, director of travel medicine at Baltimore’s Mercy Medical Center, tells TIME. But if you don’t feel like even touching the table (Gerba does, but Zimring says he doesn’t bother), avoid eating food directly off the surface.
“My food will stay on a paper plate or wrapper,” adds Zimring.
Air vents and seatbelt buckles
Two plane features with frequent usage (that may not receive a regular cleaning) also make the list.
The air vents above each seat are great for circulating ventilated air to each passenger, but the TravelMath testing found 285 CFU/sq. in. on their dials — more bacteria than on the plane toilet flush buttons.
The seatbelt buckles similarly had 230 FCU/sq. in., which isn’t surprising since every passenger touches their buckle at least two times during the flight.
Gerba recommends bringing a small bottle of hand sanitizer on the plane and using it periodically.
But Gerba points out that with roughly 50 people to a bathroom, they’re still an easy way to pick up an infection. He found the fecal coliform E. coli on some of the sinks, flush handles and toilet seats he tested. TravelMath found that the flush buttons had 265 CFU/sq. in. (but no fecal coliform bacteria).
“It’s hard to beat the restroom,” in terms of germiness, Gerba says, “because the water shuts off so people can’t complete hand washing.” The sinks are so small, he adds, that people with large hands can’t even fit them fully underneath the faucets.
Zimring recommends using a paper towel on the door latch on the way out, and says that’s the one precaution he never fails to take.
Passengers have been known to treat the pocket on the seat in front of them as a wastebasket, stuffing trash, dirty tissues, used diapers and more into the pouch.
On planes with quick turnarounds on the ground, cleaning crews may not even get a chance to empty out the seat pockets, let alone disinfect the cloth. And one Auburn University in Alabama study found that MRSA germs survive for up to 7 days on seat pocket cloth — the longest it survives on any of the hard and soft surfaces the researchers tested.
Drexel University Medicine only recommends one way to avoid germs in the seatback pocket: “Just don’t use them. It’s simply not worth the risk.”
Choosing the aisle seat lets you get up whenever you feel like it, but that freedom comes with a little more risk.
The tops of aisle seats are likely harboring germs from every person who walks by them and holds on for support, according to Zimring — and many of those people have just come from the bathroom. So be aware of touching the area next to the aisle headrest, and it’s probably best to not rest your face there as you fall asleep.
Sitting near the aisle puts passengers in the line of fire of any communicable viruses that could break out on the plane.
One study published in Clinical Infectious Diseases analyzed a flight from Boston to L.A. that made an emergency landing due to an outbreak of vomiting and diarrhea. The researchers found that that people sitting in the aisle were far more likely to contract norovirus, but there was no link between contracting it and using the bathroom.
“If you sit by the window seat you have less chance of getting sick,” Gerba confirms.
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