How air travel affects the body and brain

Despite the fact that air travel has long become a common occurrence, scientists have only recently begun to study its effects on the human body.

A tiny bouncing screen, rattling sound, and frequent interruptions – watching a movie during a flight is not exactly a pleasant experience.

However, people who fly more often find that they or others experience unusual emotional responses when watching even the most innocuous films during a flight.

Even such positive comedies as “Bee Movie,” “Bridesmaids,” or “The Simpsons” can bring tears to passengers who usually wouldn’t cry when watching such films on the ground.

Physicist and TV presenter Brian Cox and musician Ed Sheeran have admitted that they are overwhelmed with emotions when watching movies in the air.

According to a new survey conducted by London’s Gatwick Airport, 15% of men and 6% of women are more likely to cry when watching a movie in-flight compared to watching it at home.

One well-known airline has even started warning its passengers that watching movies on board may affect their emotional state.

There are many theories explaining why air travel makes a person more vulnerable and prone to tears—sadness from being separated from loved ones, anxiety about the upcoming trip, or homesickness.

However, there is also evidence that the flight process itself impacts a person’s psyche.

Data from numerous studies indicate that flying at an altitude of 10 kilometers above the ground in a pressurized metal tube can strangely affect our consciousness, alter our mood, sensory perception, and even cause itching.

“In the past, there was little research on this topic because the effect is not a major problem for healthy people,” says Jochen Hinkelbein, president of the German Society of Aerospace Medicine and deputy director of emergency medical care at the University of Cologne.

“But with the increase in popularity and decrease in cost of air travel, planes are now used by older and less healthy people. This has brought more attention to studying this area,” Hinkelbein adds.

Undoubtedly, the airplane cabin is not the most suitable place for a human: the air pressure is equivalent to that at the summit of a 2,400-meter-high mountain.

The humidity is lower than in some of the driest deserts, while the air pumped into the cabin is cooled to 10°C to compensate for the excess heat generated by passengers and all the electronics on board.

Reduced pressure in airplanes can decrease the oxygen levels in passengers’ blood by 6-25%. In hospitals, such a drop typically necessitates the use of an oxygen mask. While healthy passengers generally shouldn’t have significant issues, this can have a substantial impact on elderly passengers and those with breathing difficulties.

Research shows that even relatively mild levels of hypoxia (oxygen deficiency) can affect our ability to think clearly.

At oxygen levels equivalent to altitudes above 3.6 km, healthy adults exhibit significant changes in memory, computational abilities, and decision-making skills.

This is why aviation regulations state that pilots must wear an oxygen mask if cabin pressure is equivalent to an altitude above 3.8 km.

Air pressure at altitudes above 2.1 km increases reaction time – bad news for those who enjoy playing computer games during flights.

Some studies indicate that at oxygen levels equivalent to an altitude of 2.4 km above sea level, there may be a decline in cognitive functions and logical thinking – this is the oxygen level typical of an airplane cabin. However, for most of us, these effects are unlikely to cause serious mental fog.

“A healthy person, whether a pilot or a passenger, should not experience cognitive issues at this altitude,” says Hinkelbein. “But if there are less healthy people in the cabin, then hypoxia can significantly reduce oxygen saturation in tissues, making cognitive impairment more noticeable.”

Hinkelbein says that the moderate hypoxia we experience during flights can also cause another, more easily recognizable effect—fatigue. Research shows that short-term exposure to altitudes of at least 3 km can increase fatigue, but some people may experience effects at lower altitudes.

“When I sit on a plane, I start to feel tired and can fall asleep more easily after takeoff,” Hinkelbein explains. “I’m not losing consciousness due to a lack of oxygen, but hypoxia is one of the factors contributing to this state.”

Another effect of low pressure is the reduction of night vision by 5-10% at altitudes as low as 1.5 km. This is because the photoreceptor cells in the retina, responsible for night vision, desperately need oxygen.

Flights also affect our sensory organs. The combination of low pressure and humidity can decrease the sensitivity of taste receptors to salt and sugar by up to 30%. A study commissioned by Lufthansa showed that spices added to tomato juice taste better during flights.

Dry air can worsen our sense of smell, causing food to lose its taste. This is why many airlines add more spices to food. And perhaps it’s fortunate that our sense of smell dulls during flights because changes in air pressure can lead to increased flatulence among passengers.

If inhaling gases from your fellow passengers doesn’t seem too strange to you, know that decreased pressure can also reduce overall comfort.

A 2007 study found that after spending more than three hours at altitudes with pressure equivalent to that in an airplane cabin, people are more likely to complain about discomfort.

Combine this with low humidity, and it’s no wonder it’s difficult for us to sit still during long flights. Research by Austrian scientists showed that long-distance flights can dry out our skin by 37%, leading to itching.

Low pressure and humidity can also intensify the effects of alcohol and contribute to worse hangovers the following day.

And here’s more bad news for those who may already fear flying:

“Hypoxia can increase anxiety levels,” explains Valerie Martindale, president of the Royal College of London Aerospace Medical Association.

But flights can affect more than just anxiety. Several studies have shown that spending time at high altitudes can lead to negative emotions such as tension, hostility, as well as reduced energy levels and resilience to stress.

“We have shown that some aspects of mood can be influenced by air pressure equivalent to altitudes of 1.8 – 2.4 km,” says Stephen Legg, a professor of ergonomics at Massey University in New Zealand, who studies the effects of mild hypoxia on people.

This can explain the increased tendency to tears while watching movies during flights, although most of the side effects occur at altitudes with lower air pressure than on commercial flights. Recently, Legg also demonstrated that mild dehydration, often encountered during flights, can also affect mood.

However, there is research indicating that altitude prompts people to feel happier.

Stephen Groening, a professor of film and media at the University of Washington, believes that this sense of happiness can manifest in tears. The boredom of the flight and the relief provided by the movie, combined with the solitude represented by the small screen and headphones, can lead to tears of joy rather than sadness, he says.

Hinkelbein has revealed another peculiar change in the human body. A new study, conducted jointly with colleagues from the University of Cologne and not yet published, showed that even 30 minutes under conditions similar to those on a commercial airliner can alter the balance of molecules related to the immune system in volunteers’ blood. This suggests that low air pressure can cause changes in immune system function.

“People are accustomed to thinking they catch a cold or flu during travel due to climate change,” says Hinkelbein. “But the cause could be changes in immune response during flight. We need to investigate this more thoroughly.”

If flights indeed alter the immune system, they not only make us more vulnerable to infections but also affect our mood. Increased inflammatory processes triggered by the immune system are associated with depression.

“A single vaccine injection can lead to mood deterioration, which typically resolves within about 48 hours,” says Ed Bullmore, head of psychiatry research at the University of Cambridge, who studies how the immune system affects mood. “It would be intriguing if a 12-hour flight to the other side of the world could induce something similar.”