The Atacama Desert in Chile is generally considered to be the driest place on Earth. The South American plateau receives little precipitation (about 15mm annually) and is virtually devoid of vegetation or animal life as a result, with humidity reaching just 10 per cent.
In a business class cabin, the average humidity is 7 per cent. In other words, it's drier than the driest place on Earth.
The arid conditions arise because the outside air that's drawn into the cabin is very cold – around -15˚C – so it can't hold any moisture. As cabin air is also frequently refreshed (roughly every two minutes) the small amount of moisture that's generated is also filtered out very quickly.
Most humidity in the cabin actually comes from passengers via exhalation. The most humid part of a plane is therefore in economy (around 12 per cent), with premium cabins suffering more. First class passengers wither in around 5 per cent humidity, while the cockpit and crew rest areas suffer from the lowest levels, with between 2 and 5 per cent humidity.
“Your body dehydrates quickly when you're
