Few things are worse than an uncomfortable seat on a cross-country flight. Unfortunately, unless you’re a seasoned traveler, you don’t have much of a chance of picking the perfect spot—at least not every time.

There’s another problem: What even is a perfect seat? Is the window seat really any better than the aisle seat? Are certain sections of the plane better for people who need more leg room? What about people with air sickness?

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Well, we hit the books, spoke with a flight attendant, and learned from a scientist to determine which factors matter when it comes to choosing your seat on a plane.

First things first: Make sure you get the chance to actually choose your seat.

“I can’t stress this enough,” Julie, a 30-year-old flight attendant in St. Louis, tells FashionBeans. “If you don’t check in, you can’t complain about a bad seat. Well, you can complain—but there’s probably nothing anyone can do about it.”

These days, most airlines allow passengers to check in online up to 24 hours in advance of their flights. For some airlines, like Southwest, your boarding position is determined by your check-in time; if you’re concerned about placement, make sure to log on as soon as possible to nab an early boarding time. Other airlines, like American, allow you to select your seat during online check-in; it’s best to do this early, as well.

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If you miss out on the early check-in and find yourself stuck with a particularly uncomfortable spot, don’t be afraid to ask the flight attendant for help.

“As long as a guest is polite, I’ll do what I can to help them,” Julie says. “We might not be able to switch their seat, but we can bring out a cushion or make sure the beverage cart comes by. We’ll do what we can to make the flight more tolerable, but again, it’s important to stay calm, smile, and treat [the flight staff] with respect.”

The seat you choose can actually affect your chances of getting sick. Sort of.

If you’re a germaphobe, or if you’re bringing kids along, you might wonder whether part of the plane is more likely to harbor infectious diseases. Fortunately, scientists have attempted to answer that question.

Vicki Stover Hertzberg, PhD, created a model to analyze the movements of “droplet-mediated” respiratory diseases on a typical passenger airplane during a transcontinental flight. Basically, Hertzberg’s team tried to determine how close you’d have to sit to an infected individual to increase your risk of sickness.

“Our model assumed an extraordinarily high infection rate,” Hertzberg says of the study. “We quadrupled the rate of infection observed in a plane that sat on a tarmac without any air circulation for 4.5 hours, a worst-case scenario.”

“When we use this particular rate in our model, it indicates that passengers at highest risk are those seated one row in front of, one row behind, or within two seats laterally to an infectious passenger. [People in those seats] are most likely to become infected, and the risk to passengers seated outside of this perimeter is very low.”

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On a typical flight, passengers seated in the aisle seats have more contacts that would enable transmission, according to the study. However, take that with a big grain of salt. To create the model, Hertzberg took samples on 10 real flights during seasonal influenza epidemics, and she says that disease transmission isn’t a serious concern.

“We took environmental samples on all flights and tested them for 18 common respiratory infections,” Hertzberg says. “All samples were negative.”

In other words, theoretically, you can reduce your risk of sickness on a flight by picking a window seat and minimizing your contact with other passengers. With that said, airplanes aren’t the hotbed of disease transmission that you might expect.

If you’re worried about getting sick, go ahead and hunker down in a window seat, if you can. But overall, you’re safe to fly without worrying about that sniffling passenger six rows in front of you.

If you’re prone to airplane sickness, you might want to avoid a few parts of the plane.

The key word is “might.” Julie, our resident flight attendant, claims that the back of an aircraft provides a slightly rougher ride.

“I tend to feel the compression, take off, and landing more when I’m seated in the back of the plane than when I am seated in the front. I guess that’s because of gravity and the landing gear.”

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Her logic isn’t completely wrong. However, the aerodynamic design of the plane plays a more significant role, especially when the aircraft encounters turbulence.

“While it doesn’t make a whole lot of difference, the smoothest place to sit is over the wings, nearest to the plane’s centers of lift and gravity,” pilot Patrick Smith wrote on his website, Ask The Pilot. “The roughest spot is usually [toward the tail]. In the rearmost rows, closest to the tail, the knocking and swaying is more pronounced.”

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Again, though, this probably isn’t a huge factor, since planes are designed to provide a smooth traveling experience for all passengers. A 2000 study failed to find correlation between seating location and airsickness, although that study only observed 38 commercial flights.

If you’re worried about motion sickness, your best bet is to drink plenty of water and eat easy-to-digest foods before your flight. In a piece published in The New York Times, physician Jennifer Derebery recommended choosing a window seat since your eyes will be able to see (and adjust to) the movement of the plane.

As anxiety also seems to exacerbate motion sickness, you might want to try relaxing with mindfulness techniques during takeoff. By keeping yourself calm, you should be able to stave off the most serious symptoms.

To ensure a comfortable flight, here are a few practical considerations.

Hopefully you’re no longer concerned with airborne illnesses or motion sickness. What’s next?

“I’d generally avoid sitting near a lavatory door, at least in an aisle seat,” Julie says. “Otherwise, you’ll be making some awkward eye contact with strangers throughout the flight, and you won’t really have better access to the facilities than anyone else. Besides, for some reason, rude passengers tend to mull around the restrooms.”

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If you’re concerned that you might make frequent bathroom trips, Julie recommends sitting a few aisles from the lavatory. In addition, aisle seats offer a big advantage over middle or window seats.

What if you’re simply looking to stretch out during your trip?

“If you’re most concerned about legroom, look out for entertainment boxes,” she says.

Entertainment boxes, by the way, are a growing trend in air travel, per a report from The Wall Street Journal. They’re hard cases filled with the computer components that power the planes’ high-end entertainment systems, and they take up a considerable amount of foot room.

The good news: The big, cumbersome boxes aren’t under every seat, so by looking ahead, you should be able to avoid them.

To further maximize your legroom, you might be tempted to sit near the plane’s emergency exit. That’s fine—provided that you’re up to the task.

“If you’re in that seat, you should be physically capable of pulling the lever and helping other passengers off the plane in the event of an emergency,” Julie says.

While emergency evacuations are rare, the hatch seat actually carries significant responsibilities. Writing for ABC, aviation analyst John J. Nance even made the case that airlines should offer free emergency hatch training to their best passengers.

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“That moment—as utterly rare as it is these days—is not the time for realizing your shoulder won’t handle 40 to 50 pounds of unhinged door,” Nance wrote.

In an emergency, the aircrew will have their hands full, so don’t count on them to step in and help. If you’re not sure whether you’re up to the task, there’s no shame in taking a slightly more cramped seat for the sake of your fellow passengers.

Considering a window seat? Keep this in mind.

If you’re a fan of the window seat, you’re in the majority; according to a survey performed by European carrier EasyJet, about 59 percent of travelers choose the window seat, while 38 percent prefer the aisle seat (very few passengers expressed a preference for the middle seat, for understandable reasons). However, not all window seats are created equal.

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“Some window seats don’t actually provide a great view,” Julie says. “On any given plane, you’ll find seats with obstructed views. If you’re looking to get that great Instagram pic, make sure you’ve got a decent window before you sit down.”

Additionally, some seats have other idiosyncrasies, from poor padding to broken reclining mechanisms. You can use websites like SeatGuru to find the worst seats on a given flight; plug your airline name and flight number into the service’s online tool, and you’ll get a (mostly) accurate seat map. As the site uses information submitted by travelers, it’s not perfect, but it’s helpful for avoiding those nightmare flights.

Remember, once you’ve chosen a seat, you’re in it for the long haul. Julie asked us to pass on one more piece of advice for your next trip.

“Stay in your seat until the plane stops moving,” she says. “I don’t care if it’s uncomfortable [right after landing]. If you already sat in it for four hours, you don’t have to stand up immediately when we’re still decelerating from a landing.”