http://www.bbc.com/future/story/20170919-how-flying-seriously-messes-with-your-
mind

By Richard Gray

19 September 2017

With the tiny screen bouncing around in front of us, tinny sound quality and
frequent interruptions, watching a movie during a flight is hardly an immersive
experience.

Yet, frequent fliers may have found themselves û or at least witnessed others û
welling up at the most innocuous of films while on a long airline journey. Even
lighthearted comedies such as Bee Movie, Bridesmaids and The Simpsons can
trigger the water works in passengers who would normally remain dry-eyed if
watching these on the ground.

Physicist and television presenter Brian Cox and musician Ed Sheeran have both
admitted they can get a bit over-emotional when watching movies on aircraft. A
new survey by Gatwick Airport in London found 15% of men and 6% of women said
they were more likely to cry when watching a film on a flight than they would
if seeing it at home.

One major airline has gone as far as issuing ôemotional health warningsö before
inflight entertainment that might upset its customers.

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There are many theories about why flying might leave passengers more vulnerable
to crying û sadness at leaving loved ones, excitement about the trip ahead,
homesickness. But there is also some evidence that flying itself may also be
responsible.

An emerging body of research is suggesting that soaring 35,000ft (10km) above
the ground inside a sealed metal tube can do strange things to our minds,
altering our mood, changing how our senses work and even making us itch more.

ôThere hasnÆt been much research done on this in the past as for healthy people
these do not pose much of a problem,ö says Jochen Hinkelbein, president of the
German Society of Aerospace Medicine and assistant medical director for
emergency medicine at the University of Cologne. ôBut as air travel has become
cheaper and more popular, older and less fit people are travelling by air. This
is leading to more interest in the field.ö

Hinkelbein is one of a handful of researchers who are now examining how the
conditions we experience on flights can affect the human body and mind.

The humidity is lower than in some of the world's driest deserts

There can be no doubt that aircraft cabins are peculiar places for humans to
be. They are a weird environment where the air pressure is similar to that atop
an 8,000ft-high (2.4km) mountain. The humidity is lower than in some of the
world's driest deserts while the air pumped into the cabin is cooled as low as
10░C (50F) to whisk away the excess heat generated by all the bodies and
electronics onboard.

The reduced air pressure on airline flights can reduce the amount of oxygen in
passengersÆ blood between 6 and 25%, a drop that in hospital would lead many
doctors to administer supplementary oxygen. For healthy passengers, this
shouldnÆt pose many issues, although in the elderly and people with breathing
difficulties, the impact can be higher.

There are some studies, however, that show even relatively mild levels of
hypoxia (deficiency in oxygen) can alter our ability to think clearly. At
oxygen levels equivalent to altitudes above 12,000ft (3.6km), healthy adults
can start to show measurable changes in their memory, their ability to perform
calculations and make decisions. This is why the aviation regulations insist
that pilots must wear supplementary oxygen if the cabin air pressure is greater
than 12,500ft.

Strangely, the air pressure at altitudes of over 7,000ft (2.1km) has been found
to actually increase reaction times û great news for those who like to play
computer games during their flight.

But there is some research that shows there can also be small decreases in
cognitive performance and reasoning at oxygen levels found at 8,000ft (2.4km) û
the same as those found in airline cabins. For most of us, this is unlikely to
cloud our thinking much though.

Flying also plays havoc with our other senses too

ôA healthy person like a pilot or passenger should not have cognitive problems
at this altitude,ö says Hinkelbein. ôWhen you have unfit people, or someone
with the flu or pre-existing problems, then hypoxia can decrease oxygen
saturation further so cognitive deficits become noticeable.ö

But Hinkelbein says the mild hypoxia we experience during flights can have
other, more easily recognised effects on our brains û it makes us tired.
Studies in hypobaric chambers and on non-acclimatised military personnel
arriving in mountainous regions have shown short-term exposure to altitudes of
at least 10,000ft (3km) can increase fatigue, but the effects could start at
lower altitudes in some people.

ôWhenever I am sitting in a plane after take-off, I become tired and find it
easy to fall asleep,ö explains Hinkelbein. ôThis is not the lack of oxygen
causing me to lose conciousness, but the hypoxia is a contributing factor.ö

Should you manage to keep your eyes open for long enough to see the crew dim
the cabin, however, then you may experience another effect of the lower air
pressure. Human night vision can deteriorate by 5-10% at altitudes of just
5,000ft (1.5km). This is because the photoreceptor cells in the retina needed
to see in the dark are extremely oxygen-hungry and can struggle to get all they
need at a high altitude, causing them to work less effectively.

Flying also plays havoc with our other senses too. The combination of low air
pressure and humidity can reduce the sensitivity of our taste buds to salt and
sweet by up to 30%. A study commissioned by airline Lufthansa also showed that
the savoury flavours in tomato juice taste better during a flight.

The dry air can also rob us of much of our sense of smell, leaving food tasting
bland. It is why many airlines add extra seasoning to the food they serve to
make it palatable during a flight. It is perhaps fortunate that our sense of
smell is diminished during flights, however, as the change in air pressure can
also lead to passengers breaking wind more often.

And if the prospect of breathing in the bodily gases of your fellow passengers
doesnÆt make you feel awkward enough, it seems reductions in air pressure can
also make passengers feel less comfortable. A study in 2007 showed that after
about three hours at the altitudes found in airline cabins, people start to
complain about feeling uncomfortable.

Combine this with the low humidity and it is little wonder we find it hard to
sit still for long periods on flights. A study by Austrian researchers has
shown that a long-distance flight can dry out our skin by up to 37%, and may
lead to increased itchiness.

For those who are already nervous fliers, there is perhaps some more bad
news.

Low levels of air pressure and humidity can also amplify the effects of alcohol
and the hangover it produces the next day.

For those who are already nervous fliers, there is perhaps some more bad news.

ôAnxiety levels can increase with hypoxia,ö explains Valerie Martindale,
president of the Aerospace Medical Association at KingÆs College London.
Anxiety is not the only aspect of mood that can be affected by flying. A number
of studies has shown spending time at altitude can increase negative emotions
like tension, make people less friendly, decrease their energy levels and
affect their ability to deal with stress.

"We have shown that some aspects of mood can be altered by exposure to cabin
pressures equivalent to altitudes of 6,000-8000ft," says Stephen Legg,
professor of ergonomics at Massey Univeristy in New Zealand, who is studying
the impact of mild hypoxia on people. This may go some way towards explaining
why passengers often find themselves crying at films more mid-flight, but most
effects in scientific studies seem to only occur at altitudes above those that
commercial airline cabins are set to. Recently Legg also showed the mild
dehydration that might be expected on a flight can also influence mood.

"We know very little about the effect of exposure to multiple mild stressors on
complex cognition and mood," he adds. "But we do know that there is a general
æfatigueÆ associated with long distance air travel, so I guess it is probably
the combined effects of these concurrent multiple mild exposures that give rise
to æflight fatigueÆ.

Then there is also research showing altitude can also make people feel happier.

But Stephen Groening, a professor of cinema and media at the University of
Washington, believes this happiness may also manifest itself as tears. The
boredom on a flight and relief given by an inflight movie, combined with the
privacy of the small screen and headphones used to watch one, could lead to
tears of joy, not sadness, he says.

ôThe configuration of inflight entertainment apparatus produce an affect of
intimacy that might lead to heightened emotional responses,ö says Groening.
ôCrying on airplanes actually consists of tears of relief, not tears of
sadness.ö

But Hinkelbein has uncovered another strange change in the human body that
could also be messing the way our bodies normally work. A new study he
conducted with colleagues at the University of Cologne, but yet to be
published, has shown even 30 minutes in similar conditions to those experienced
on a commercial airliner can alter the balance of molecules associated with the
immune system in the blood of volunteers. It suggests the lower air pressure
may cause a change in the way our immune systems work.