Captain Lim Khoy Hing explores the strange effects of dry cabin air.
Words: Captain Lim Khoy Hing
A guest once wrote to me for tips on overcoming the problems caused by dry air. He asked if the air in the cabin could be the reason his nose often bled while flying.
Air inside an airplane can indeed be very dry. Cabin air has a very low relative humidity of around 10 per cent. Compare this value to the Earth’s desert regions where humidity is around 20 to 25 per cent. However, if you are in a tropical region, for example, in Singapore, the average relative humidity is about 85 per cent.
In the dry environment of the cabin, evaporation of moisture from the skin can be as high as eight ounces of water per hour! According to some medical sources, those with very sensitive skin may find that the delicate sinus inside the nose tends to dry out fairly quickly. This may cause the nose to bleed.
Dehydration may also be the cause of cracked lips, as well as a burning sensation in the eyes, headaches and lethargy. Less obvious consequences of dehydration include inducing stress on the body, reducing mucus production and lowering the body’s immune system.
To keep hydrated, drink a lot of water while onboard. It is recommended that an adult should drink at least eight cups or one litre of water for every hour in the air. Beverages such as alcohol and coffee should be avoided, as they act as diuretics, further dehydrating the body. While flying, one should eat foods that are low in salt and sugar, to help the body retain moisture. Finally, be sure to carry a small tube of moisturising lotion to avoid the irritation of dry, flaky skin.
If nosebleeds still occur in flight despite following all reasonable precautions as above, it may be necessary to request the assistance of the cabin crew or arrange to see a doctor after landing.
In spite of what I have outlined above, there are conflicting views amongst the scientific community as to the main cause of nosebleeds in flight. As one doctor commented, if dry air and low humidity were indeed the case, then all inhabitants living in very cold regions of the world and where humidity is very low should experience frequent nose bleeding, as would the majority of air passengers and cabin crew.
Other views state that nosebleeds are the result of a common cold or upper respiratory tract infection. In actual fact, because the nasal blood vessels are very fragile, any irritation to the delicate sinus tissue may cause a bleed.
It has also been shown that there is barely any difference in the incidences of nosebleeds between people working long hours in cold storage rooms of food processing factories, those working in air-conditioned rooms with low humidity and others working in normal environments.
TRUTH ABOUT CABIN AIR
Although cabin air may be dry, rest assured, it is very clean. On all modern aircraft, passengers and crew breathe a mixture of fresh and recirculated air. Using this combination rather than fresh air makes it easier to control temperature and helps maintain a certain level of humidity.
Occasionally, on some flights, you would notice a strong odour – a smell similar to the exhaust – in the cabin, shortly after pushback. Usually, this only happens when the exhaust air is drawn into the air conditioning system when the engine is started. The wind is often to be blamed because it causes the air to backflow through the air conditioning system. This normally lasts only a minute or so, until the engines are running and have stabilised. It may be unpleasant but it is little different to the fumes you sometimes breathe in your car while stuck in a traffic jam.
Studies have shown that a crowded airplane is no more germ-laden than other enclosed spaces. In fact, the under floor filters have been described by manufacturers as being of hospital quality.
According to Dr Tom Finger, Professor at the University of Colorado School of Medicine, dry air can affect how we perceive aromas. “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, you lose much of the flavour component of food.”
The low humidity and the ‘dried-out’ sinus cavities may explain why, sometimes, food may taste different in the sky, as compared to on land. You may find that your favourite snack that you snuck into the flight, no longer tastes the same – a good reason not to try to sneak outside food onboard!
Taking into account how aroma affects taste buds, AirAsia actually enhances the flavour of in-flight dishes to ensure guests are always served flavoursome delights in the air. Of course, when you touch down at AirAsia’s many amazing destinations, you can always get your local fix.
Captain Lim Khoy Hing is a former AirAsia Airbus A320 and AirAsia X A330/A340 pilot who also used to fly the Boeing 777. He has logged a total of more than 25,500 flying hours and is now a Simulator Flight Instructor with AirAsia X. In his spare time, he shares his opinion on aviation issues with others. For more air travel and aviation stories, check out his website, ‘Just About Flying’ at at www.askcaptainlim.com.
Captain Lim’s book, LIFE IN THE SKIES, which won third place in the Reader’s Choice Award at the Malaysia BookFest 2015, and its Mandarin version 【飞行日记】 are now available for purchase onboard all AirAsia and AirAsia X flights. Enjoy these great collections of articles by a veteran aviator.