Effects of Dry Air
Already after 3 hours of flying the relative humidity is as low as 5 % in a typical First Class Cabin. In an airplane, the only humidity contribution comes from the people on-board. Ironically, the lower seat density – the lower is the humidity. In other words, premium passengers paying the most are exposed to the driest air.
In theory the human body tolerates great variations in humidity. But there are limits. According to our knowledge, many independent medical studies prove that the ideal relative humidity for the human body is in the range of 20%-60%. Conditions onboard an aircraft rapidly gets extreme. After less than one hour’s flight the air resembles that of a desert climate. In First Class air humidity can get below 5% RH. This is because outside-air mixing replenishes the cabin air constantly. Replenishment assures that the recirculated portion does not endlessly recirculate but is rapidly diluted and replaced with outside air. During cruise or on the ground, the outside air is drawn in at the same rate that cabin air is exhausted out of the airplane. When approx. half of the air at cruising altitude is coming from outside via the engines where the air is extremely dry, the blended cabin air will get dry.
The longer the flight continues, the drier the air becomes and the more evident the symptoms become. When people are subjected to air humidity lower than 10-15% they experience a series of different problems. For example sleep disorders, dry eyes, tiredness, dehydration of the skin and mucous membranes. De-hydration is a well-known dilemma on long-haul flights that quickly unbalances essential body functions and rapidly put humans in an alarming condition. The body is stressed and the feeling of un-comfort is very distinct. Really long flights amplify the effects. Pilots and flight attendants who are subjected to these conditions day in and day out are extra exposed. And over-time, the wear and tear body effect can be apparent.
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.
According to NBC, Dr. Tom Finger, Professor at the University of Colorado School of Medicine and co-director of the Rocky Mountain Taste and Smell Center, claims that:
“Dry air doesn’t help our sense of smell, either. Typically, odorants are transported to olfactory receptors in the nose via the mucus lining. When the nasal cavity is dried out, the efficiency at which odorants are detected by the brain is reduced. When you “lose the olfactory component,” explains Finger, “you lose much of the flavor component of food.”
It is medically proven that extremely low RH levels make the human body functions abnormally being more sensitive due to dehydration and human senses, such as taste, are very different. Even short time exposure to extremely dry air affects the nose and mouth. In fact, up to 80% of what we consider taste is actually derived from smell. The taste is built up around many very complex co-existing factors.
Why food tastes differently in the sky can partly be explained by:
– Dry air changes the taste in the mouth
– Dry air alters the viscosity of the saliva
– Dry air result in swelling of the mucous membranes
– Dry air modifies the ability to vaporize into the nose
– Dry air de-hydrates nasal cavity affecting the sense of smell (innervation/olfactory nerve)
– Dry air decreases volatility of odor molecules