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Raise your hand if you’ve ever felt the long-haul hangover. You know the feeling — after spending several hours on the plane, you pull yourself onto the jetway tired and queasy, with a foggy head and slight headache. You feel gross and not just because you need a shower. While some might blame this general state of ickiness on jet lag, germs or recycled air, the reason we feel so lousy after a long flight actually has more to do with chemistry — specifically, how our bodies react to the change in chemistry that happens miles above the ground. Here’s a look at four key factors that play into this, and four tips for making it easier.

Elevation

You might be flying at 35,000 feet, but the cabin is usually pressurized to feel like you’re at 6,000-8,000 feet, or roughly the elevation of Machu Picchu. If you live on a coast and are used to being at sea level, that hangover feeling you get when you’re flying is likely just mild altitude sickness — if you’ve ever taken a trip to the mountains to hike or ski, you’re probably already familiar with the symptoms, which include headaches, fatigue and nausea. When you’re scaling a mountain, the general wisdom is to go slowly and let yourself acclimate, which unfortunately, you can’t really do when you’re flying. While not everyone is susceptible to getting sick from high altitudes, the reason some people do has to do with oxygen — or rather, the lack thereof — which brings me to my next point.

Oxygen

Air at sea level looks different than air at higher altitudes — for starters, it’s a lot heavier. The molecules are packed more densely, which means you take in more oxygen with every breath. The higher you go, the farther those molecules spread apart and the less oxygen you breathe in. We oxygen-dependent humans don’t often respond well when we can’t get the amount we need and flying for hours at a time — breathing in the sparser air — can cause your body’s internal oxygen levels to drop, which, in turn, can make you tired and affect your ability to concentrate or think clearly. Sitting for long periods of time doesn’t help either. When you’re motionless, your blood tends to pool in your legs and feet and you become less efficient at circulating the oxygen throughout your body and to your brain, exacerbating symptoms.

Photo by izusek / Getty Images.
She really should have read the rest of this article… Photo by izusek / Getty Images.

Compression

When a plane makes its descent, the systems controlling the pressure inside the cabin are turned off, causing it to fluctuate as it tries to match the pressure outside, making the air expand or contract. Have you ever noticed that your bottle of water “explodes” a little when you open it mid-flight or collapses in on itself before touchdown? The same thing happens to the gases inside your body and it’s what makes your ears “pop” during descent or your sinuses start to hurt, especially if you have a cold. A similar thing also happens to the gases in your intestines and stomach, which you can thank for the general feelings of nausea or lack of appetite. The presence of gas inside your dental fillings can expand, too, which can sometimes lead people to get toothaches toward the end of a flight.

Dehydration

The air pulled in at high altitudes is much dryer than on the ground, so during the flight, you’re exhaling moisture-rich air and inhaling dry air. If you don’t replace the water you’re losing, it can lead to dehydration. More than just chapped lips or dry hands, dehydration can cause headaches, dizziness and, unsurprisingly, irritability — though that last one typically is more common for kids and babies. Some planes are dryer than others — the Boeing 787 Dreamliner, for instance, has an upgraded filtration system that allows for more humidity in the air. The difference compared to other planes is modest (think Phoenix rather than the Sahara) but every little bit helps.

What You Can Do to Feel Better

Move About the Cabin

Fidget, get up, walk around, step from side to side in the aisle — basically, do anything you can to move your muscles at least every 30 minutes. Not only will this help you get your blood flowing and send oxygen to your brain, it will also help reduce your risk of other potentially serious health issues associated with sitting for too long.

Avoid Alcohol

It’s true that it’s easier for you to get drunk on a plane. That’s because — to oversimplify the science a little — your cells are already having a hard time taking in enough oxygen at higher elevations and alcohol makes them even less efficient. Drinking alcohol can also lead to dehydration because it makes it harder for your body to retain and reabsorb water. A drink at the airport bar or an in-flight Bloody Mary might make you feel good in the moment, but it’ll likely make you feel crummy later on.

Photo by Richard Kolker / Getty Images.
Remember, it’ll hit you faster in the air. Photo by Richard Kolker / Getty Images.

Drink Plenty of Water

And not just during the flight. Drink more than your usual amount the day before and in the hours leading up to a flight to give yourself a leg up before breathing in all that dry air. Better yet, make sure you bring a big bottle of water with you, too, to sip from throughout the flight. The hydration is good for you and getting up to use the bathroom frequently will keep you from sitting too long, so it’s a win-win.

Relieve Minor Symptoms

If you have any nasal congestion, consider taking a decongestant before or during your flight to help avoid sinus pain during descent. Sipping water — another reason to hydrate! — chewing gum, sucking on a piece of hard candy and forcing yourself to yawn can also help relieve ear pressure. But if you’re still having trouble popping your ears, try holding your nose and mouth tightly and exhaling forcefully. If you’re prone to in-air nausea or abdominal discomfort, try to steer clear of heavy, deep-fried foods in the hours leading up to your flight and opt instead for lighter meals and healthy snacks. Your stomach will thank you.

Featured image by kieferpix / Getty Images

Know before you go.

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