In the old days when people traveled by boat, horse and carriage, train, foot, or by any other means of transport that used reasonable speeds to get from one place to another, sinus problems weren't a big issue. You don't hear Gilgamesh or Odysseus or Beowulf complaining about their sinuses en route. Maybe they were too macho for that, or just too busy worrying about outwitting gods and monsters. But it's also likely their sinuses were fine because they had time to adjust.
It's with the age of jet travel that you began hearing about a problem some people call aerosinusitis or barotrauma. Birds have all kinds of cool adaptations for dealing with zooming along at high altitudes, but the human body, sadly, does not. Our sinuses loathe air travel for a couple of reasons.
First, changing air pressure. When a plane lifts off and descends, it travels through layers of atmosphere with drastically different air pressures. Your sinuses are, essentially, a series of connected air pockets in your skull. You're only comfortable when the air inside those pockets and the air outside your head is of equal pressure.
So when a passenger jet suddenly jumps thousands of feet in the air, the air in your sinuses doesn't have time to adjust, and you feel the pressure difference. If you've got any kind of sinus issues, it's going to hurt, probably a lot. Congestion of any kind will make it harder for your sinus air to equalize with cabin pressure, and from there your problems will just snowball. The Eustachian tube, which connects the back of your nose to your ear, could get plugged up, which could lead to ear pain and ringing.
As if that's not bad enough, there's also the cabin air, which, thanks to high altitudes, is literally as dry as a desert. Actually, at roughly 12 percent humidity, it's a lot drier than the Sahara, which is typically a balmy 25 percent [sources: Smith, University of Utah]. Sinuses don't like really dry air because it can irritate and inflame their delicate mucus membranes.
Meanwhile, germs are swarming all over bathroom door handles, faucets, armrests and tray tables. Those little critters love nothing better than irritated, inflamed mucous membranes in a nice, warm locale. In other words, if you didn't get on the plane with sinus issues, you stand a better-than-average chance of disembarking with them.