is there any place on earth with humidity lower than inside an airplane?

[Richard_Pearse]

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The recirculation process in modern commercial aircraft manufactured by Boeing and Airbus […] saves a lot of fuel: The amount of fuel consumed by jet engines also depends upon the respective air supply volume. The more air that is drawn off for the air- conditioning system, the higher the fuel consumption. By re-using some of the air from the cabin interior, the amount of air diverted from the engines is reduced. Recirculation provides another big advantage for passengers and the crew: at high altitudes the external air contains very little moisture due to its low temperature. Every person gives off moisture, which evaporates in the air. While in an empty cabin the relative air humidity is only about two per cent, in a full cabin it increases 15 per cent during a long-haul flight. The low level of humidity has the side-effect that pathogens are very quickly inactivated.

In order to raise the humidity levels, several hundred kilograms of water would have to be carried on a long-haul flight, which would greatly increase fuel consumption. In addition, condensation caused high temperature differences between the aircraft and its surroundings would flow into the insulating layer concealed behind the cladding in the cabin. It would absorb it, causing corrosion in very inaccessible places. Humidification systems are under development, but it will be some time before they are available. Until then, passengers can simply compensate for the low humidity levels in the cabin by drinking plenty of water or fruit juice during a flight. Alcohol, caffeine or carbonated drinks should, however, be kept to a minimum.