Why is the air in planes so dry?

[Susie28]

Hi there!
I'm back from a vacation which included a 3 hour flight in Europe. The vacation was great (too great!!), but the flight was horrible. I used my MEGs - but they helped only a little bit. After 1 hour I had to close my eyes for the rest of the flight:-(
Is it possible that the air in planes is more dry than the air of "normal" air conditions? Normally, my MEGs work good in air-conditioned places. But on the other side, I never stayed longer than 1 hour in an air-conditioned place. I avoid air condition and use the MEGs for shopping or traveling with the bus or train. But in this cases I only stay for ca. 1 hour in the air conditioned place.
Could it be that the MEGs stop to work after 1 hour? Or did they just not work because of the very very bad air in the plane?
Whats different in airplanes? Why is the air soooo dry there? Do you have some advice for me?

[djb]

When you are flying at high altitudes, air is pumped into the cabin through an air-conditioning/heating unit. Part of that unit is called the "water separator". It removes moisture from the air so that everything works OK in the air system. Too much moisture in the air used in the aircraft causes unwanted problems (water will drip out of the air outlets on to your head if the water separator doesn't work). I don't know if humidity levels in the cabin are even considered when designing a plane (perhaps in expensive private jets?). Commercial jets make sure you have O2, heat, & air-conditioning.

[longhorngal]

Hi! I recently took an international flight to Korea... my eyes were dry with my MEGs on, but I was just dehydrated in general after the flight. I think about it this way... my eyes would probably be even more dry without my MEGs. I am dreading the very very long flight home this Friday!!