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A Head-to-Butt-to-Toe Explanation of What Happens to Your Body on an Airplane

“If man was meant to fly, he’d have been given wings,” says the old mantra we ignore every time we step through the metal detector and head for the bar in the departure lounge. But there’s some truth to it: Nothing about humans flying is natural, and since we’ve only been doing it for a little more than 100 years, our bodies haven’t adapted to the very particular set of stressors we’re putting on them. So if you’ve ever wondered what’s making your stomach churn, your ears pop and your legs cramp, here’s what that pressurized, B.O.-scented environment is doing to us.

Your Brain. Besides the mental anguish when the only in-flight movie option is Batman v. Superman, many people also experience a sense of panic as the plane takes off. “Oftentimes, this is trauma-related, but it may not come directly from trauma during flight,” explains clinical social worker Veronica Acevedo. “For example, if you had to fly to attend a funeral, those feelings may manifest again during another flight, without you realizing that’s where the anxiety comes from.” News stories about plane crashes or terrorism may also cause “vicarious trauma,” adds Acevedo, where people develop anxiety by being exposed to events through the media.

Meanwhile, many people get headaches just from being on a plane. “This airplane headache is due to the difference in pressure between the cabin and the sinuses of the person,” explains S. N. Jagadesh Kumar, a doctor for Spicejet Airlines at Chennai International Airport, India. The good news is that this headache usually vanishes as soon as you get off the plane.

Your Eyes. So what’s all that pressurized air doing to your eyes? According to aerospace medicine specialist Diego M. Garcia of the Aerospace Medical Association, “Pressurization systems in most commercial flights nowadays literally inject recycled air from the engines to the cabin.” Predictably, this air is pretty dry, which can dehydrate the eyes and, “in extreme cases, might cause infections and corneal damage,” says Garcia.

Your Ears. To understand why your ears pop during a flight, it helps to understand something called Boyle’s Law. It’s a little technical, but in a nutshell, as pressure decreases, the volume of gas increases. This includes the air in your middle ear, which expands uncomfortably as the pressure in the cabin drops. “The middle ear and eardrum behave as a cavity full of air, which expands and compresses when the plane and the pressurized cabin ascends and descends,” explains Garcia. The popping you experience is the pressure equalizing between your ear and the cabin — you can experience this relief more quickly by chewing gum, since the motion made by the jaw when chewing helps to open up this passageway, releasing the air faster.

Your Heart. Since the untimely death of Carrie Fisher, some have questioned whether flying may have played a role in her heart attack. While it’s impossible to know what may have happened to Fisher if she hadn’t been flying that day, “conditions like hypertension, arrhythmias or coronary disease may be worsened by hypobaric hypoxia [the decrease in oxygen at altitude],” explains Garcia. Those with a healthy heart have nothing to worry about, however.

Your Lungs. “Most pressurized aircraft have air pressure […] equivalent to the pressure at the top of a mountain 8,000 feet above sea level,” explains Garcia. “This reduces the amount of oxygen available for ventilation.” This will have little effect on healthy lungs, but can potentially be serious for those with preexisting respiratory ailments.

Your Immune System. Unsurprising, but still gross: Because of all those strangers in tight proximity, “It’s easy to get communicable diseases [say, a cold] from sick travel mates sitting next to each other,” says Garcia. While most of us believe this is due to the recycled air, it’s more likely to do with the surfaces everyone touches — from E. coli on the toilet seat in the restroom to the MRSA superbugs on the tray tables, the entire plane is crawling with other people’s germs. Bottom line: Carry hand sanitizer.

Your Gut. Boyle’s Law rears its head once again, only this time it’s applying its gas-expanding principles to your bowels. “As the atmospheric pressure decreases on ascent, the gas bubbles in our body get bigger in size,” explains Anna-Maria Carvalho, a physician and medical consultant for Air Canada. “The gut has a lot of gas, and all that gas increases in size at altitude, which is why you feel bloated. This will be especially evident if you down a can of soda just before getting on the plane — all those tiny gas bubbles sitting in your stomach will get bigger in size on ascent.”

So know that if your seatmates are enjoying a Diet Coke on takeoff, you can expect to be smelling their gas for the rest of the flight.

Your Butt. Sitting for all that time can you give you something known as a numb butt. “Blood and fluids tend to slow down [during a flight] causing stasis, which creates numbness and stiffness,” explains Garcia. Planes aren’t exactly conducive to a pleasant stroll, but even just walking to the restroom a couple times might help wake up those sleepy cheeks.

Your Legs. During flight, you face an increased risk of deep-vein thrombosis — that is, the formation of blood clots in deep veins, such as in the legs. For a few reasons, explains Carvalho: The first risk is simply from sitting down for so long, which causes the blood to pool in your legs. “Secondly, if you’re either very short or very tall, the veins behind your knees may get kinked while you sit on an airplane seat, further decreasing blood flow.”

So what can we do about all of these issues? Apart from trying to move around a bit, which may help with any numbness and circulatory issues, and drinking water, which Carvalho says forces you to walk to the bathroom to pee, there’s not much you can do but chew gum, cut back on soda and avoid news stories about aviation disasters. Plus, for the average, healthy person, most of these problems are both minor and short-term, so your best bet is just to grit your teeth and try to fall asleep.

Or you could try watching Batman v. Superman until you brain melts — whichever works for you.