Air travel has become an increasing source of pain, discomfort and illness among passengers and crew members in recent years. It has been suggested that health problems for long distance fliers are far more common than the airlines and aviation safety officials either know or are willing to admit. Difficulties in documenting their extent starts with the rapid dispersion of the passengers to many different points. Also, it is often hard to separate the effects of forced contact with airborne infectious organisms from the immune-suppressing effect of travel-related stress, which leaves people more vulnerable to infection. The rapidity of air transport, for example, results in disturbances of the circadian rhythm in aircrews and passengers who have to travel long distances.
To economize on fuel, the newer airplanes change cabin air less frequently -- every six minutes instead of every three minutes on older models. This may mean that only 40 to 60 percent of the cabin air is renewed during the flight. Complaints have been made of headaches, nausea, double vision and the discomfort of breathing stale air. Dehydration, due to dry cabin air, decreased consumption of water and the dehydrating effect of other beverages, can cause general discomfort, digestive problems, undue fatigue and worsened jet lag. Low humidity levels (typically of around 10%) can cause eyes to become sore and red and the upper respiratory passages to dry out, increasing their susceptibility to infection. Airsickness, and fainting following hyperventilation provoked by anxiety, are not uncommon.
Lack of movement, cramped seats and the pressure of seat cushions on the back of the thighs impairs circulation in the legs, often result in swollen ankles and feet and sometime in dangerous blood clots in the lower leg than can, days later, break loose and lodge in the lungs (causing flight-related pulmonary embolism dubbed called "economy class syndrome".
Cabin pressure corresponds to a height of between 1,800 to 2,000 metres above sea level. This low pressure hinders the exchange of gases in the lungs, reducing oxygen intake unless the heart and lungs work faster. It is also more difficult for the lungs to expel nitrogen, which concentrates in the blood stream and contributes to the swelling of limbs. Variations in pressure during the flight may result in injuries to the ear, the sinuses, and sometimes the teeth. As the plane descends and outside pressure builds, the Eustachian tube in the middle ear tends to collapse and the middle ear may fill with fluid and blood, and even rupture if the Eustachian tube is blocked with the mucous of a cold or upper respiratory infection.
But the most frequent hazard is constituted by the accidents, usually slight but sometimes serious, caused by turbulence.
To counter disease-bearing pests, certain governments require flight attendants to spray d-phenothrin 30 minutes before landing at airports in the Caribbean, South America and South Pacific. Whilst of low toxicity to humans, the insecticide can create problems for people with allergies, chemical sensitivities, asthma and other conditions. Symptoms of headaches, nausea, fatigue, seizures, and in extreme instances, memory loss, cognitive skills loss or a depressed immune system, have been claimed by passengers and flight attendants.
In 1979, influenza struck 72% of passengers on a flight to Kodiak, Alaska, after the plane had been held at its landing gate for four hours. The common source of their infection was determined only because nearly all the sick passengers visited the same doctor in Kodiak.
On a 1986 flight from San Francisco to Hawaii, more than 100 of the 486 passenger and crew members had headaches and nausea, a problem attributed to the poor quality of cabin air recirculated though dirty filters.
There are now numerous cases reported of flight-related pulmonary embolism in otherwise healthy adults. A Melbourne law firm has 800 Australians on its books who want to sue 20 global airlines over "economy class syndrome" (deep vein thrombosis) with many more were likely to sign up as the condition receives greater publicity.