Taking a flight or going for a drive that's longer than three hours? Then let's talk about blood clots. Why, you ask? For some travelers, blood clots can be a serious risk during long-distance trips, according to the Centers for Disease Control and Prevention. And recently, a fight broke out on a flight when a passenger with a history of blood clots allegedly couldn't get past another passenger to exit the plane after it landed, TMZ reports.

Roughly one in 1,000 people will develop a blood clot, according to the CDC. And immobility — like the kind you experience on a long trip — is a big risk factor, Thomas Maldonado, M.D., vascular surgeon and professor of surgery at NYU Langone Medical Center, tells SELF.

Here's what you need to know to protect yourself.

Blood clots typically form in the deep veins of the body.
Blood clots are also known as deep vein thrombosis, as they typically form in the deep veins of the body that aren't visible through the skin. Most often, they form in the legs, though they can occur in any vein, Maldonado said. What makes a blood clot dangerous: the potential for it to move through the body's circulatory system.

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"The situation is simple plumbing: You have arteries that bring the blood to the extremities, then you have veins return the blood back to the heart," Dr. Maldonado said. "When a clot forms in the veins, the clot can dislodge and travel back towards the heart and lodge in the lungs or heart."

If that happens, it can be dangerous — or even fatal.

Long-distance travel is a risk factor for blood clots because it involves sitting for prolonged periods of time.
While many associate blood clots with just flying, there's actually an increased risk for blood clots during any type of long-distance travel. "There’s nothing magical or special about flying at 33,000 feet that predisposes you to a blood clot," Maldonado said. "When you’re immobile for more than three or four hours at a time, you can develop a clot because blood tends to pool in the legs." People who are on prolonged bed rest also have an increased risk of blood clots.

When we’re sitting for a long period of time—and not engaging our leg muscles by stretching or walking — the mechanism that keeps blood flowing smoothly doesn’t work per usual. "Our calf muscles propel the blood back [to the heart and lungs], in addition to the natural circulation of the heart pumping," Dr. Maldonado said. "But when you’re on a long plane trip, you tend to be cooped up and immobile, and that’s a major risk factor."

He added that people often become dehydrated on long trips, too, which is another risk factor for blood clots. When the body doesn't have enough fluids, blood vessels can narrow while blood can thicken, increasing the risk for blood clots.

The signs and symptoms of blood clots are pretty unique—if you have one, you’ll know something’s wrong.
"If you have a tender or painful leg, oftentimes in the calf, and it starts to swell, those are things that could make you suspect that you might have a blood clot," Maldonado said. Skin that is warm to the touch and redness of skin are also symptoms of deep vein thrombosis, according to the CDC.

If you're experiencing one or more of these symptoms during a long-distance trip, Maldonado said it's not a "four-alarm fire" and a reason to rush off the plane, but the sooner you get the area checked out — typically by ultrasound — the sooner experts can diagnose a potential clot and intervene with treatment to prevent fatal complications. People with blood clots typically have to take blood thinners for three to six months to prevent their clot from growing and prevent new clots from forming. Sometimes, "clotbusting" medication is also needed to break up a clot.

While pain and swelling in the leg are, of course, uncomfortable symptoms, Maldonado said the clot traveling is still the most concerning issue. "That’s really what you want to avoid," he said. "And there’s not a good way to predict which clot will travel, but when you have a blood clot in the leg, you can develop a pulmonary embolism, and about a quarter of those people will die."

A pulmonary embolism occurs when a blood vessel in the lungs is blocked by a clot. "The pulmonary embolism symptoms are very traumatic," Maldonado said, and they include chest pain, shortness of breath, and difficulty breathing. If you're experiencing these symptoms, he said to seek help immediately. Pulmonary embolisms are also treated with clot dissolvers and blood thinners. But if the clot is very large and life-threatening, surgery might be necessary.

Thankfully, there are ways to prevent blood clots.
"The real key to blood clots is to understand your risks," Maldonado said. Risk factors include a family history of blood clots, pregnancy, taking birth control, smoking, being overweight or obese, having inflammatory bowel disease, and being over age 60, according to the Mayo Clinic.

If you have a series of risk factors — and you're going to be immobile for a long period of time — it's important to take steps to prevent a clot.

Prevention is simple: On a long-distance trip, try and stretch your legs and walk every few hours. If you're on a long flight, take advantage of those "the captain has turned off the seatbelt sign" moments and take to the aisle to get your leg muscles working. If you can't get up, try to at least move your lower legs—without kicking the seat in front of you, of course. The Mayo Clinic suggests raising and lowering your heels while keeping your toes on the floor, then doing the opposite by lifting and lowering your toes while keeping your heels still.

Maldonado added that if you have a series of blood clot risk factors, you should stay away from dehydrating drinks like alcohol and caffeinated beverages while traveling and make sure to drink enough water. Compression socks are also helpful to wear when traveling, as they can help keep circulation moving.

Bottom line: You can prevent blood clots from forming, and you should know your risks and take the necessary precautions when traveling.