In theory the human body tolerates great variations in humidity. But there are limits. Conditions onboard an aircraft rapidly gets extreme. After less than one hour’s flight the air resembles that of a desert climate. Normally the relative indoor humidity in homes and offices is between 50-60%. In an aircraft it drops to 5-15%. This is because half of the air is drawn in by the engines at a height of around 10,000 m where the air is extremely dry. As a result, skin, eyes and linings of the mouth and nose dry out. Long flights amplify the effects. Pilots and flight attendants who are subjected to these conditions day in and day out are extra exposed.
Dry air causes:
•Cold and allergy symptoms
•Dry skin and eyes
•General fatigue and discomfort
•Increased jetlag impact
The longer the flight continues, the drier the air becomes and the more evident the symptoms become for the Crew. When people are subjected to air humidity lower than 20% they experience a series of different problems. For example sleep disorders, dry eyes, tiredness, dehydration of the skin and mucous membranes.
Other discomforts include the need to remove contact lenses, increased likelihood of colds, a greater risk of viral infections, as well as problems with dry skin and allergies. This is particularly wearing for the Crew, who are constantly subjected to the dry air. Increasingly longer flights, now with durations up to 18 hours, only aggravate the symptoms.