Aside from delays and annoying passenger antics, most flights go off without a hitch. But, on occasion, you might find yourself on a flight where a fellow traveler has a medical emergency. That’s what happened on a 2016 American Airlines flight from Honolulu (HNL) when Brittany Oswell suffered a pulmonary embolism, more commonly called a blood clot.

Sadly, she died from the incident. And incredibly, she’s not alone.

According to the National Blood Clot Alliance, an average of 274 people die from blood clots every day and 600,000 nonfatal blood clots occur every year. Air travel can increase this risk as you’re sitting for long periods with little room to move your legs. This can cause a particular type of blood clot called deep vein thrombosis (DVT).

“DVT’s are more likely to form when there is venous stasis, which means that the blood is pooling in the veins,” Dr. Mehmet Oz (of “The Dr. Oz Show”) told The Points Guy. “This is more likely to happen in people who are sedentary for long periods, like on a long plane ride, because part of the way the blood in the leg veins gets back up to the heart is when muscles contract.”

In 2018, Dr. Rajiv Narula, MD — founder of the International Travel Health Consultants — told TPG that “on flights more than eight hours, [there’s an] increased risk of DVT.” And certain studies say this condition can occur on flights as short as four hours.

While the condition can resolve itself, in some cases people experience a pulmonary embolism: when the clot travels to the lungs and blocks blood flow there. The blocked blood flow in the lung prevents the body from getting oxygen.

So, how can you tell if you have a blood clot on a plane? We chatted with a couple of experts to learn the symptoms, find out who is most susceptible and what to do if you develop one during a flight.

Related: It’s flu season — Here’s how to avoid getting sick on a plane

Know if you’re at risk

According to Dr. Narula, travelers with certain “underlying medical issues” are typically more prone to DVT.

Several factors can make a person more susceptible to developing a blood clot. “Things that put you at risk for blood clots include certain genetic clotting disorders, being immobilized because of surgery or injury, chronic diseases like heart failure and cancer, smoking and older age,” said Dr. Oz.

Dr. Nathan Favini, medical lead at Forward, a new technology-based healthcare startup, added that oral birth control pills and pregnancy also make a blood clot more likely. “Estrogen is thought to be the cause,” he said. “So, forms of birth control that don’t contain estrogen, like IUDs, are safer in this regard.”

If you fall into one of these categories, you should take extra precautions to help prevent blood clots and be aware if you start to develop any symptoms.

Related: What happens if you get sick during a flight?

Symptoms of a blood clot

Knowing you have a blood clot can be tricky, as you can often write off the symptoms as something else, but there are a few key warning signs to pay attention to when traveling. If you experience these symptoms, you should seek medical help immediately.

“If you develop pain, tenderness, swelling, warmth and/or redness in your legs during a flight, those may be signs of a deep vein thrombosis or blood clot,” said Favini. “If you have more than one or many of those symptoms, it becomes more likely that you’re experiencing a clot.”

When former TPG social media director, Lindsey Campbell, developed a blood clot during a six-hour flight home from Iceland, she woke up with sore and aching calves, and felt dizzy, hot and light-headed.

The other thing to look out for, according to Favini, is the rapid onset of shortness of breath. This can be a sign that a clot has formed in, or traveled to, your lungs. “If you’re experiencing these symptoms, especially shortness of breath, let the staff on your airplane know right away,” said Favini.

Related: I got food poisoning before my long-haul flight

How to prevent a blood clot

So, now you know what to look for if you’re developing a blood clot. But, there are certain critical steps you can take to avoid one in the first place.

“Drink lots of fluids, but not with caffeine, which makes you pee more so [there’s] less fluid in your blood … And avoid alcohol,” said Dr. Oz. “Then, move around every two hours and move [your] feet like stepping on a gas pedal more frequently.”

When TPG spoke to Daniel Giordano, co-founder of Bespoke Treatments Physical Therapy in New York City, about movements and stretches travelers can easily perform on an airplane to promote blood circulation, Giordano said he recommends his clients travel with a device such as a Firefly knee strap. This can gently stimulate the peroneal nerve to promote circulation while performing simple exercises like, as Dr. Oz suggested, pumping your legs.

And for Dr. Narula, the key is anti-embolism socks. These knee-high stockings are specifically designed to put graduated pressure on your legs, which can improve circulation.


This story was originally published on The Points Guy. Sign up for the TPG daily newsletter and wake up to unbeatable flight deals, travel industry news, and credit card bonuses that let you travel first-class to some of the world’s most incredible destinations at a fraction of the price.