It seems almost inevitable that when you fly on an airplane, you get sick shortly thereafter. Most blame the germs circulating in the air, but the cause might actually be the surfaces you're touching. To find out how dirty planes and airports are, Travelmath, an online trip calculator, performed an informal study, sending a microbiologist to swab areas at five airports and on four flights performed by two major carriers.

The scientist collected 26 samples, which were stored in sterile broth and sent to a lab to determine just how many illness-causing bacteria were present per square inch, measured in colony-forming units (CFUs). As Mashable reports, “Tests were performed on different items at each airport and on each plane, and then ranked by the median of the results."

According to Travelmath, the results showed that the surfaces in planes and airports are dirtier than some surfaces and objects in your home—and the dirtiest place of all is the tray table:

1. Tray table: 2155 CFU/sq. in.
2. Drinking fountain buttons: 1240 CFU/sq. in. (airport)
3. Overhead air vent: 285 CFU/sq. in.
4. Lavatory flush button: 265 CFU/sq. in.
5. Seatbelt buckle: 230 CFU/sq. in.
6. Bathroom stall locks: 70 CFU/sq. in. (airport)

Surprisingly, bathrooms were actually cleaner than many other places, probably because they’re regularly swabbed down. This might also be why no samples tested positive for E. Coli, a fecal coliform.

It's important to keep in mind that, though the results are interesting, this isn't a peer-reviewed study appearing in a scientific journal. It's not clear exactly what bacteria Travelmath was testing for, and, as Mashable points out, "the presence of bacteria does not necessarily mean that those exposed to it will get sick." Still, it can't hurt to take the commonsense approach to traveling that Travelmath recommends: Throw out any food that touches the tray, and make sure to carry hand sanitizer.

Here's a handy infographic that breaks all of Travelmath's findings down:

[h/t Mashable]