Air travel can pose health risks - even some deadly ones - but there's a lot you can do to protect yourself

The most common health risk from flying: the common cold, flu, and similar viral infections.

Airplanes put a ton of people in a small enclosed space together. If someone sitting near you has a cold, there's a high chance of you being exposed to that. Especially if they're coughing and sneezing.

There's also the fact that planes aren't fully sterilized in between flights, so germs from a previous passenger could still be on surfaces like armrests or tray tables.

Compounding the problem: the stress, exhaustion, and dehydration that come with travel can make you more susceptible to catching the cold.

Dr. Umesh Gidwani, Chief of Cardiac Critical Care at The Mount Sinai Hospital, suggests that travelers worried about colds and germs bring hand sanitizer, or even cleaning wipes, on their next flight.

"You can get a pocket-sized Purell and keep your hands clean," he said.

(Disclosure: This reporter worked at the Mount Sinai Health System for several years.)

If you're especially concerned, you can also choose to wear a face mask, he said. That's especially a good option for people who might be more susceptible to catching a cold.

"People might not want to, because they find it stigmatizing, but if you're really concerned about a virus, or if it's flu season, it's always an option."

A less common but more serious risk: deep-vein thrombosis, or DVT.

DVT is a condition that occurs when blood clots form in the large veins deep in your legs. While it can happen to virtually anyone, immobility, particularly in an upright seated position, can significantly increase the risk.

DVT doesn't just develop on flights: it can also develop on long car rides, train trips, and anywhere else that you sit for long periods of time without getting up.

"There's nothing magical about being 30,000 feet in the air," said Dr. Thomas Maldonado, Medical Director of the Venous Thromboembolic Center at NYU Langone Health. "It's more the fact that you tend to be cooped up, sedentary, immobile, and often dehydrated when you fly."

Symptoms of DVT can include aching, pain, swelling, and tightness in the leg, especially in the calf, according to Dr. Darren Schneider, Chief of Vascular and Endovascular Surgery at NewYork-Presbyterian Hospital and Weill Cornell Medicine.

In some cases, the blood clot can "chip off like a pebble in a stream and travel to the lungs," Dr. Maldonado said. That's called a pulmonary embolism, or PE, and is life-threatening. According to Dr. Maldonado, of the million Americans who are diagnosed with DVT or PE each year, about 100,000 die.

Other factors that increase your risk of developing DVT are dehydration — common on planes — smoking, genetic factors, obesity, past leg injuries, age and a history of some cancers. Another risk factor: taking hormonal birth control.

"But all these things can get magnified, or add up, traveling on a plane," Dr. Maldonado said. "So if you traveled by plane, and developed sudden pain in the calves, or swelling in the legs, that can be an important tip off."

There are a few things you can do to reduce your risk — some airlines even provide tips, Dr. Gidwani said

Leaving your seat to walk around periodically — even once every hour or so — can go a long way. Even doing exercises at your seat can help, like stretching your legs, flexing your ankles up and down, and clenching your calves.

Wearing knee-high compression socks can help, as can keeping hydrated — grabbing a large bottle of water at the airport can help with that. Avoiding alcohol can also help, Dr. Schneider said.

If you're concerned, talk to your doctor before flying. They may suggest taking an aspirin (or a baby aspirin) before your flight.

If you experience leg pain or swelling in your calf after a flight, you may have developed a DVT. Call your doctor to get it checked out.

If you develop any shortness of breath, chest pain, or sudden sharp pain, you may have a pulmonary embolism. This is a life-threatening condition, so call an ambulance or head to your nearest emergency room.

If your flight involves crossing time zones, you might experience jet lag.

Jet lag results from the body's circadian rhythm being interrupted. It most commonly causes trouble sleeping and fatigue, but can also cause minor stomach problems, anxiety and irritability, headaches, nausea, and more, according to the CDC.

The best way to manage jet lag is to try and start adjusting to your new time zone before leaving for your trip.

Make sure to be as well-rested as possible, stay hydrated, and avoid eating unhealthy foods.

There's another issue to keep in mind.

Air travel is inherently stressful, both mentally and physically. The chaos of the airport, boarding, and getting settled; loud noise from the engines and cabin climate-control system; pressure changes as the plane climbs and descends; sodium-heavy foods; and dehydration, combined with dry cabin air, can all take a toll.

Those with existing or undiagnosed health conditions that are exacerbated by stress should be cautious. It's theoretically possible that pressure changes from takeoff and landing could also exacerbate certain heart or lung conditions, Dr. Schneider said.

"If you have severe emphysema or lung disease, like congestive heart failure, those could potentially be exacerbated by the altitude.

"People with COPD, for instance, should take special considerations with their oxygen when they fly," Dr. Gidwani added.

If you have any concerns, check with your doctor before you fly.

Also, remember that unless you have a specific health concern, getting or developing any serious health issues from a flight is extremely rare. Taking care of yourself, and making sure to move around to avoid a DVT, are the best ways to stay safe and healthy.