How flying impacts on your health

Flying affects your body


Did you know that a six-hour flight has the same effect as sitting atop an 8,000 foot-tall mountain in the Atacama Desert (which by the way, is the driest place on Earth)? Well, it does.

This post will explain the negative impact that flying in a commercial airline has on your body.

When you fly, you are exposed to the combined effect of low atmospheric pressure (and therefore less oxygen), very dry cabin air and inactivity due to the fact that you are sitting immobile for several hours.
Add to this (in the case of long flights), lack of sleep due to the cramped seating arrangements of modern aircraft, and the outcome is that you will feel tired and maybe even dizzy during a flight.

atacama-aircraft dryness are the same 15 percent humidity

The cabin of an airplane is as dry as Atacama Desert. A. Whittall

If you add alcohol or caffeinated beverages (Coke, Pepsi, coffee or tea) you may even feel much worse.

You can’t avoid all of these factors, but there are some things that you can do to minimize some of their side effects:

1. Low Air Pressure during the flight

Your body is adapted to working at sea-level atmospheric pressure, which is equivalent to a column of water 33 feet (10 meters) high pressing down on you. This is a pressure of 14.7 psi (pounds per square inch) all over your body.

As you move up, away from sea level, this pressure falls for simple reason that there is less air mass above you, pressing down on you.

You don’t usually notice this difference in pressure, that is, as you climb in altitude you will not feel lighter. However the pressure drop experienced as you climb has an important consequence on your body.

As pressure decreases so does the quantity of molecules in a given volume of air (for the nerds among my readers, this is expressed by Boyle’s Law). And less molecules of air means less quantity of oxygen and this is the cause of what is known as “Altitude Sickness”: at higher altitudes there is simply not enough oxygen in the air for your body to use. (This is what happens to those who try to climb the Everest, and to most people who go above an altitude of 6,550 ft. (2,000 m).

But aren’t planes pressurized?

Yes, but….

At the normal cruising altitude of an airplane (35,000 ft., or 10.650 m) atmospheric pressure drops to 3.8 psi, which is roughly one-quarter of the sea level pressure. This means that the quantity of oxygen in the air is also 26% of that found at sea level. This amount of oxygen is far too low and could lead to death due to hypoxia (lack of oxygen).

For this reason aircraft cabins are pressurized, but, and this is the “Big Secret”, they are not pressurized to sea-level values for cost reasons!.

Let’s explain this in detail:

The structural strength of the airplane determines how much differential pressure the cabin can tolerate (Differential pressure is the difference between the internal and external pressures).

Aircraft can withstand pressure differentials of about 8 psi. Yes, they could be built to withstand higher pressures but they’d be stronger, with more resistant materials and therefore much heavier. Weight is crucial, as a heavier plane would use more fuel, becoming far too costly to fly.

For this reason, airplanes are pressurized to an intermediate value between dying of hypoxia and sea level pressure.

The limit is imposed by the external pressure at cruising altitude (35,000 ft.): 3.8 psi. So, with a maximum differential pressure of 8 psi, the inner pressure can’t exceed 11.8 psi.

This pressure of 11.8 psi is equivalent to flying at an altitude of 6,214 ft (1,894 m). Which is quite reasonable as it falls below the limit which makes most people feel uncomfortable.

This altitude has roughly 81% of the oxygen content you have at sea level. So, it is a tolerable trade-off.

For this reason air flight regulations limit the maximum cabin altitudes to 8,000 ft. (2,440 m). But do airlines comply?

A study which analyzed 204 flights found that the average value of air pressure complied with this limit but, some airlines flew with a higher altitude: the maximum value was 8,915 feet (2.717 m), which can be distressing to some passengers.

Hypoxia – lack of oxygen

With the 6,214 food limit you should not have nasty side effects (hypoxia) because most people start to notice the effects of lack of oxygen at altitudes beyond of 8,200 ft (or 2.500 m).

But unfortunately, some of its milder symptoms can be felt by sensitive people at lower altitudes.

These side effects include sleep disruption, oliguria (the medical term for peeing less), a racing heartbeat (tachycardia), dizziness and even nausea.

To make matters worse, sitting in the cramped seats that modern airlines confine its passengers to, for several hours, and not drinking enough fluids can cause additional health risks.

Being immobile and dehydrated can reduce blood flow to your legs, reduce oxygen levels in your body’s cells and cause localized hypoxia.

All of these factors may make you feel faint if you stand up all of a sudden during a flight. So you should do so slowly, and flex your arms as you stand up. You should get up, walk down the aisle and to the “gym” movements suggested by your airline’s magazine or media recommendations. It will keep blood flowing and minimize the risk of thrombosis (blood clots).

In-flight flatulence

Yes, farting is another side effect of low pressure. Reduce the pressure and gases expand: a volume of 100 ml at sea level becomes 130 ml at (6,000 feet – 1.830 m). That is a 30% increase in volume for ALL gases, and this includes those gases located inside your body cavities: for instance your middle ear. This lower pressure is what makes your ears pop with altitude.

Normally air expands and flows from your ear to your throat through two tubes (Eustachian tubes), and this equalizes the pressure gradually, however if this happens all of a sudden it causes a popping sound.

Very Important tip. If you have a nose, sinus or ear infection, the congestion will upset this flow of air and you may feel pain. It could even rupture your ear drum: Avoid flying if you have these conditions.

Expanded gases inside your gut, will bloat you, and also your fellow passengers. This means that you will all pass more gas inflight. Unfortunately, farts are part of the airline cabin experience! whether you fly business or economy class!

How to prevent bloating (and farting)

Try to eat foods that reduce flatulence before you fly: rice, dairy products and fish are ok. Keep away from peanuts.

A bloated stomach can be uncomfortable: Stay away carbonated drinks before flying; if you drink a soda before takeoff, the gas will be trapped in your stomach and, as the plane climbs, it will expand by 30%, stretching your tummy.

2. Extremely Dry Air

As we said, the cabin air is pressurized, and the process that pressurizes it makes it very dry:

The aircraft’s turbofan (jet) engines compress a stream of air, this heats it, so it then has to be cooled. Which eliminates humidity (which at 30,000 feet is already very low, roughly 1% water content).

Then it is then mixed with air that is recirculating from the cabin (yes, with flatulence included). Its temperature is adjusted to keep it comfortable for the passengers.

The only source for humidity (water) in the aircraft is the original humidity of the cabin air when the plane took off. Add to this the moisture that is lost by the passengers and crew as they breathe and perspire during the flight.

So, relative air humidity during a flight is very, very low!

Those interested in the facts should read this paper and this article.

Air humidity decreases inside the cabin to values of around 10 to 15%. And the longer the flight, the drier it gets.

This value is lower than the relative humidity of the Driest Place on Earth, Atacama Desert in Chile

which averages 17.3% RH!


Atacama Desert is very dry! – David Bebber

Risks caused by the dry cabin air

Your body is used to an average relative humidity of around +60%, which is the typical value in temperate countries so this extremely dry in-flight atmosphere hurts you. These are the negative side effects of very dry inflight air:

  • According to this paper flu virus survive for longer, and also spread much more easily in dry air.
  • Your nose will dry out and this will irritate your sinus membranes. The same happens to your throat and bronchial system. If you suffer from asthma keep your medication handy.
  • It will also dry out your eyes (your tears will evaporate faster in the dry air), and this loss of moisture will irritate your eyes. During a flight you should use glasses instead of contact lenses and use moisturizing eye drops.
  • Your skin loses far too much moisture and will become dry. Keep it moisturized with lotion or cream and also use lip balm.
  • Your body loses water due to evaporation (as you sweat and also, as you breathe). You can become dehydrated! Less water makes your blood more viscous (thicker) which means that your heart has to pump harder to circulate it through your body. Blood flow becomes more inefficient which causes oxygen levels to drop slightly inside your body’s cells. Also waste toxins build up inside the cells.

    Blood stagnation is worsened by sitting for long periods of time: it accumulates in your feet and lower legs, which swell and may produce blood clots This is very dangerous.

    So please, get up, flex your feet and walk to the back of the plane frequently. It will keep blood and oxygen flowing through your legs.

Read more about how to avoid Dehydration.

Closing comments

You should drink one glass of water every hour you fly, avoid booze and caffeine and carbonated beverages (the gas will make you feel bloated)

Get up and walk around the cabin regularly, flex your muscles and move your feet.

Always ask for water when you fly. Not coffee. just plain and simple water

© 2018 Patagonia Wellness – A. Whittall


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