'Always cry on planes? Same. I just found out there's a scientific reason why.'

We all know that babies cry on planes. But have you ever noticed that there are grown-ups sniffling and wiping away tears beside you? Are you one of them?

You are not alone. I am also one of them. I would be hard-pressed to think of a time I haven't cried on a plane. And it turns out there are scientific reasons we do this.

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It's happening in your brain.

The physical conditions inside the aircraft cabin have a real, physiological effect on our emotions.

Neuroscientist Dr Tara Swart gets right to the biological root of our in-flight emotional turmoil. "For some people, travel makes them nervous, but hypoxia is the main differentiator in air travel in terms of impact on the brain physiologically," she told CN Traveler.

"The lower than usual air pressure causes mild hypoxia in the brain (low oxygen levels). These affect our cognition and make us less able to regulate our emotions and manage stress. This is usually manifested by people crying when watching sad movies or generally feeling on edge."

But lack of oxygen isn't the only culprit. Dehydration can get us feeling emotional too.

And ccording to the World Health Organization, air pressure in flight cabins typically sits about 6,000 to 8,000 feet above sea level, which can lead to — you guessed it — dehydration.

James Roy, from Brainworks Neurotherapy, told CN Traveler mild dehydration often results in "mood imbalances and feeling more emotional".

This might explain why I get so teary mid-flight — or after a large night out, when I'm similarly dehydrated.

The science behind our mid-air emotions.

Roy added that our emotional responses during flights aren't just random. "Air travel may involve emotional triggers, such as saying goodbye to loved ones or coming back from a stressful business trip, in addition to travel fatigue.

"These emotional triggers, combined with the discomfort of travelling, can make people feel more vulnerable."

This perfectly explains why that return flight after visiting family always leaves me a blubbering mess. It's not just the goodbye — it's the whole package of exhaustion, discomfort, and emotional vulnerability.

What science says about plane tears.

Jodi De Luca, a psychologist who studies the impact of high altitudes, offered additional insight into why we get so teary at 30,000 feet.

"There's a lot that goes into simply getting on a plane, including travelling to the airport, getting through security, depositing luggage and keeping track of time. That pressure — coupled with possible thoughts of never seeing loved ones again in the rare event of a crash — adds up, no matter how much a person tries to 'intellectually process it' through logic," she told TIME.

Jodi pointed out that the lack of control we experience while flying plays a significant role. "We have little control over our environment while we are travelling by plane," she said. "Although we may not be consciously aware of our emotional vulnerability, our emotional brain is working overtime."

Why we choose tearjerkers at altitude.

I always choose the SADDEST movies to watch on planes. Clickbaiting myself to cry. Some top titles include My Sister's Keeper, Marley and Me and Love Actually. Self-torture.

Apparently, I'm not alone in my masochistic in-flight entertainment choices. A 2017 survey of passengers commissioned by London's Gatwick Airport found that 15 per cent of men and six per cent of women are more likely to cry while watching a film on a flight than if they were to watch that movie elsewhere.

Jodi had an explanation for this too.

"Movies can be a particular trigger for people once a plane has taken off. The darkness of a flight cabin illuminated by the small screens playing whatever an airline has to offer can make a person realise they are truly alone until landing," she said.

Plus, as Dr Tara pointed out, the hypoxia from lower oxygen levels makes us less able to regulate our emotional responses to those tearjerker scenes.

Don't forget to pack the tissues.

So the next time you find yourself sobbing into your complimentary airline pretzels over a rom-com that wouldn't make you bat an eye at on solid ground, know that it's not just you — it's science.

The combination of emotional triggers, physical changes in your brain from the altitude, and that feeling of being suspended between destinations all contribute to those mid-air tears.

Maybe pack some extra tissues in your carry-on. Your altitude-affected brain will thank you.

Are you a plane cry-er? Share in the comments below!

Feature Image: Supplied.