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There's no better time than now to start planning your next trip this holiday season. However, what's not so great about traveling this time of year is the likelihood of returning home from your destination with more than complimentary pretzels and fond memories. Getting sick at least once during fall and winter is, arguably, inevitable, especially for frequent flyers. It's totally understandable, really, when you consider the fact that airports and planes are basically a cesspool of germs.

If you're wondering why illness always seems to strike before, during, or after a trip, the answer comes down to what you touched, what you drank on board, and how (or if) you slept properly when vacationing. Here, medical and travel experts weigh in on the five ways in which flying the friendly skies can wreak havoc on your immune system. No worries, though, we've also included six precautions you can take to avoid getting sick on your travels.

1. Stress

Traveling can be stressful in and of itself, but packing for a trip while you're already feeling under the weather can be even worse!

"Stress can wear down on your immune system," said Dr. David Greuner, Surgical Director at NYC Surgical Associates. "On top of that, many people tend to stray away from their healthy habits while traveling when it comes to food, alcohol, and getting enough sleep—all of which can take a toll on your health and your body's ability to ward off illness."

2. Exposure

Coming in contact with other sick passengers in the security line, at the flight gate, or when boarding the plane increases the chance of transmission.

"In an airport, with so many people touching the escalator rail, the chair arms, or computer screens, there is the chance that someone who is ill may have just wiped his or her nose, and is now checking in for a flight at a kiosk," said Dr. Dana Hawkinson, infectious disease specialist at the University of Kansas Health System. "As you touch those surfaces, then inadvertently rub your mouth, nose, or eyes, you can become infected."

In addition to proximity to other people, the airplane cabin and bathrooms can also serve as a breeding ground for germs and illness-causing bacteria.

"Many germs are spread through the air, so any time someone coughs, sneezes, or talks, you may be at their mercy," said Taranath. "Airplane bathrooms are some of the filthiest places on flights. But germs can also lurk in other unsuspecting places on an airplane, like tray tables, magazines, air conditioning knobs, and headrests, where they can live for up to a week if surfaces are not properly cleaned."

3. Not Getting Enough Rest

Trust us, we know just how excited you are to go sightseeing on your weekend getaway, but not taking the time to properly rest once you land can put your immune system at risk.

"Many people taking a vacation may forget that travel itself can be exhausting," suggested Dr. William Spangler, Global Medical Director for AIG Travel. "Walking long distances with luggage in tow or losing a few hours of sleep can wear down even the fittest travelers. And breaking from healthy routines, such as eating wholesome food and exercising regularly—in addition to jet lag and changing time zones—may weaken travelers' immune systems, increasing their risk of illness."

4. Low Humidity

Sure, the air-conditioning system in the airplane cabin helps to prevent most germs from being circulated through the cabin. But all that compressed air comes with a cost: low humidity.

"Low cabin humidity, which is caused by low humidity at high elevations, is not something the human body is well-equipped to handle," said Taranath. "Low cabin humidity causes the nose and throat to dry up, leaving the body's natural, first line of defense— called mucociliary clearance—down for the count, thus creating an opportunity for germs to sneak through."

Airplane Food Trays
Credit: Juan Silva/Getty Images

5. Not Staying Hydrated

"A hydrated body is more prepared to fight infections that may be caused by germs that you may have been exposed to," said Taranath. "It's also worth noting that, while low humidity can cause external dryness and discomfort, there is no evidence to suggest that it causes internal dehydration, so there is typically no need to drink more than usual. However, it can be helpful to avoid caffeinated and alcoholic beverages, which act as diuretics."

Useful Methods to Prevent Post-Travel Sickness:

1. Take your vitamins.

"Take some extra Vitamin C and/or Zinc prior to, and during, the flight," recommended Taranath. "These nutrients can help bolster our immune systems to also fight infections better."

2. Check in with the Centers for Disease Control (CDC).

If your wanderlust takes you out of the country, Amesh A. Adalja, Senior Associate at Johns Hopkins Center for Health Security, suggested that travelers should look at the CDC website to "understand what infections are present at one's destination and what countermeasures one can imply, such as medications, vaccinations, insect repellants, etc."

3. Stick to your normal routine on vacation.

"When traveling try to stay in your routine of eating healthy, drinking in moderation, and getting enough sleep to help make sure you stay healthy," advised Greuner.

4. Always wash your hands or use wipes.

"Keeping a small container of sanitary wipes or hand sanitizer can help clean your hands after utilizing the restrooms, or prior to handling in-flight food or beverages, which could be one of the most unsuspecting ways we allow germs to get into our bodies," Taranath urged.

According to Dr. Gustavo Ferrer, who is also the author of Cough Cures, "handwashing is like a 'do-it-yourself' vaccine," involving these five simple steps: wet, lather, scrub, rinse, and dry. You can also rinse your nose with a saline solution like Xlear Nasal Spray to decrease the adherence of bacteria and viruses.

"Regular handwashing, particularly before and after certain activities, is one of the best ways to avoid getting sick," said Ferrer. "It's a win for everyone, except the germs."

5. Avoid touching your face.

"Germs often spread when you rub or touch your face and nose," Ferrer added. "Resist the urge! We transmit germs from around the nose and mouth by getting in contact with our own secretions."

6. And, if all else fails, stay home.

"People can work to make traveling safer by rescheduling their trips, as feasible, when they're sick," suggested Spangler. "Travel insurance, which—in addition to connecting travelers with resources if they fall ill while they're traveling—can protect passengers for covered reasons."