If you avoid airplane bathrooms for fear of germs, it's time to rethink your strategy. Travelmath sent a microbiologist to swipe airplanes and airports to find the dirtiest spots and the results are as surprising as they are gross. The ickiest spot on a plane is actually a seat's tray table, with an average of 2,155 colony-forming bacteria units per square inch across four planes, reports Business Insider. The overhead air vent was also fairly gross with 285 units per square inch, followed by the toilet flush button with 265 units. But compared to the button on an airport drinking fountain—1,240 units—both were squeaky clean. (More airplane stories.)