Mile Cry Club: The science behind why we weep more easily on planes

Have you ever cried at a film on a long-haul flight? If so, you’re not alone.

The prevalence of high altitude weeping is because your tear ducts are a tad more sensitive in the air than on the ground.

According to a study conducted by Virgin Atlantic, 44 per cent of male passengers confess they have "buried themselves beneath a blanket" to hide their damp cheeks during a flight. Women in the same situation were more likely to pretend they had "something in their eye", the survey found. Understandable - it's fairly awkward to start bawling in the company of complete strangers.

Overall though, more than half of the respondents said that, yes, they had experienced heightened emotions at 35,000 feet, enough that Virgin actually started issuing warnings before films of a particularly tear-jerking nature. So why is this a thing? It’s a peculiar phenomenon but does have some basis in science. Telegraph Travel investigates.

Why do we cry anyway?

Even this question is something of an enigma. Why do certain emotions trigger the excessive spilling of fluid from our eyeballs, in the same way an onion would? It’s a trait seemingly unique to humans. Some scientists suggest it's an evolutionary behaviour associated with bonding. Crying encourages others to step in and comfort us, which strengthens social bonds.

According to biochemist William H Frey, who studied this extensively during the 1980s, women cry five times more often than men. This could be down to the hormone prolactin, which is associated with the prompting of tears and is found in higher concentration among females.

A propensity to crying might also be linked to nationality, as suggested in the journal Cross-Cultural Research, which looked at 35 countries and found that women in richer countries including the US and Sweden were slightly more prone to crying than those from developing countries such as Nigeria and Nepal.

That cathartic feeling we have after a good sob? That could very well be down to the neurotransmitter leucine enkephalin, which is emitted when we cry and happens to be a natural painkiller.

So why are we more likely to blub on planes?

Good question. Most psychologists to have commented on the topic suggest it’s because flying puts us in a vulnerable state. We don’t consciously want comfort and reassurance from our fellow passengers (that would be weird), but the primitive corner of our brain might be suggesting we try to forge useful allies while in a precarious situation miles above the ground.

GP Dr Nick Knight, who has a special interest in lifestyle medicine, tells Telegraph Travel: "Having a cry is a complex business, triggered by anything from the benign and insidious to the abundantly obvious.

“Sticking yourself in an unfamiliar environment 30,000 feet off the ground and therefore away from your comforts of everyday life, surrounded by strangers and even stranger sounds, sits nicely on that spectrum.

“Sprinkle in your likely altered human physiology with lower air pressures and oxygen levels and your body and mind is promoted to go into emotional lability.”

He adds: “Is there concrete evidence? No. Is there plenty of anecdotal evidence? Yes. Will crying on a plane harm you? Only if you happen to watch The Notebook.”

What does it have to do with cabin air?

The air at high altitudes is thin, and oxygen levels very low, so aircraft have clever systems in place to keep cabin pressure at a level equivalent to an altitude of around 5,000-8,000 feet.

However, this still leaves us with lower levels of oxygen in our blood than we'd have on the ground and therefore leads to a number of consequences: tiredness being one of them.

Tiredness is another factor than can knock our emotions and leave us more vulnerable to a sob-fest.

Could in-flight entertainment systems be to blame?

One reason we might cry more freely onboard a flight is that although we are are indeed packed like sardines into a flying tin full of strangers, modern in-flight entertainment systems do quite a good job of "cocooning" us into a feeling of solitude.

Behavioural psychologist Jo Hemmings remarks: “The sense of isolation we feel mid-air, with headphones on and a screen just a few feet from your face, will amplify the chances of emotional arousal. You are far more likely to cry in this situation than in your own home.”

As for letting these tears fall despite being in the company of random neighbours? This enclosed-space-isolation environment can also foster a response known as "stranger intimacy", as one academic paper points out - Crying while Flying: The Intimacy of Inflight Entertainment.

It has been observed in several social studies that humans have an odd tendency to share more with strangers in terms of private facts and emotions than they might with well-established friends and family.

“We’re more likely to cry if we fly on our own, rather than with someone we know,” agrees Hemmings.

Does flying make us feel like children?

“We become more child-like when we fly,” Hemmings notes. "We’re waited on and looked after by air stewards, who effectively take on a guardian-like, nurturing role and so we respond to that by behaving as a child might, with little reign or control over our emotions.”

Throw into the equation the fact that many journeys by air are associated with a major event, where you may be leaving a loved one behind or indeed going to visit one, Hemmings points out, and you’ve got another reason to be feeling more emotional than usual.

Does alcohol play a part?

It doesn’t help that many of us are partial to an alcoholic beverage (or three) to pass the time on a lengthy flight, and the effects are thought by some scientists to be stronger at altitude - although the jury’s out on this. If nothing else though, the fact that you’re strapped to a chair as you nurse your supply of wine rather than sauntering around a bar with it means you’re metabolizing it more slowly.

Drinking in of itself renders us more liable to express myriad emotions, as I think we can all agree, and that includes crying. So stir a cocktail into the chemical cauldron? Welcome to the Mile Cry Club.