We all know that planes can be nasty, germ-ridden places.
They cart around hundreds of passengers each day and often back-to-back without much time for a thorough cleaning.
And when there is time for a clean, the most obvious places will get priority - such as the bathrooms.
This is why, according to an investigation by TravelMath who sent a microbiologist to gather samples from flights, tray tables were discovered to be the dirtiest place on an aircraft. Yep, where you eat from.
But if tray tables are really just fold up Petri dishes, it also begs the question of how filthy your plane seat really is.
Using the same logic, you would assume that the seats, like the tray tables, aren't necessarily priority when it comes to giving the aircraft a quick once-over between flights.
And unfortunately, it's true. Plane seats are pretty disgusting.
According to Thrillest, a plane is lucky to get a quick vacuum or have each of the seat pockets emptied between shorter flights.
It often isn't until an overnight stay at an airport that crews can actually wipe down the armrests, tray tables and in-flight entertainment screens, vacuum the floors, and clean out the seat back pockets.
But deep cleaning - which would include the seats being dry-cleaned, shampooed or sanitised - happens even less regularly.
United Airlines told the Wall Street Journal that their planes are deep-cleaned only every 35 to 55 days. American reported every 30 days, and Delta every 90 to 100 days.
That's plenty of time for dirt, and who knows what else, to build up.
In fact, plane hygiene tests commissioned by The Today Show in the USA in 2014 revealed that plane seat belts were filthy, including one that showed the presence of "human bacteroids".
"These are bacteria that live in our gut and our intestines. These are dangerous bacteria that cause serious infections", Dr. Robert Glatter, an emergency doctor at New York's Lenox Hill Hospital told the show.
Another study conducted by Auburn University found that harmful and potentially deadly bacteria like MRSA and E. coli survive for days on arm rests, toilet flush handles, tray tables, window shades, seats and seat pockets.
So next time you fly, be sure to pack some sanitiser and wash your hands regularly.