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.