No wonder your eyelids feel like sandpaper after a few hours inside an aircraft, your sinuses hurt and you're dreaming of water like an Alaskan malamute on a hot day.
An aircraft cabin is dry. Drier than the driest place on our planet.
A study by the University of Palermo in 2013, which measured relative humidity on different aircraft aboard a large number of short flights, found levels in the range 1.8-18.5 per cent aboard Boeing 767, Airbus A320 and A340 and DC9 aircraft.
Relative humidity in May, the driest month in the Gobi Desert, averages 23 per cent.
At Maria Elena South in Chile's Atacama Desert, reckoned to be the driest area of the hyper-arid Atacama desert, scientists recorded mean atmospheric relative humidity of 17.3 per cent. That's about as dry as Mars.
One aircraft that advertises its high humidity cabin as a selling point is the Boeing 787, which has a relative humidity of about 15 per cent.
So when the cabin crew come around with the water bottles, do yourself a favour and take two.