Diseases and Disorders > Chronic Conditions

Traveling for the Holidays? Avoid Deep Vein Thrombosis on the Plane

Taking the combination pill may increase your risk of developing a blood clot on a long flight.

A woman walks down the aisle of a plane with her carryon suitcase in tow.

Published: December 20, 2023

Key Points:

Sitting for an extended period—such as during a long-haul flight—can cause blood to pool in your lower legs, increasing your risk of developing a blood clot and pulmonary embolism (PE).
Estrogen-containing contraceptives can change the way blood coagulates, raising the likelihood of clots.
If you take combined hormonal contraceptives or have other risk factors, take steps to help reduce your chances of getting a blood clot or PE.

If you're preparing to fly home for the holidays, some common worries may prance around your head like spiteful reindeer. Are you going to make your connecting flight? Will you run into your ex at the supermarket? How will you politely dodge eating your aunt's "famous" green bean casserole? How will you avoid blood clots?

Wait. Blood clots?

They're probably not top of mind. According to many people on TikTok, though, they should be—especially if you take combined hormonal contraceptives.

A recent viral video claims people who take estrogen-containing birth control are at increased risk of deep vein thrombosis (DVT) or blood clots when flying long distances. DVT is a form of venous thromboembolism (VTE) that usually develops in the lower leg.

It's highly treatable but in some cases, it can lead to a deadly pulmonary embolism (PE) or stroke.

Is TikTok right about potentially getting deep vein thrombosis on a flight?

Generally, TikTok isn't the most reliable source of health advice. If you're an avid consumer of social media, you probably know that eating raw carrot salad isn't going to cure your PMS or help with your hormonal problems, and your teeth probably won't fall out if you get pregnant, for starters.

DVT on a flight, though? There is some truth to this particular claim.

Simisola Olatunde-Adeyemo, a physician associate with the United Kingdom's National Health Service (NHS), warned the masses of the potential risk by responding to another user. The first user said her fiancé–a doctor–advised her to stand up and move every two hours during a long flight because she's on the combined pill.

"I've been seeing this video around and absolutely love it," Olatunde-Adeyemo said in her video response.

She then explained that taking estrogen-containing contraceptive pills can slightly increase the risk of DVT, particularly during long-distance travel. Stretching and walking around every couple of hours and wearing compression socks can also help mitigate that risk.

"Research indicates the risk of VTE increases about three times when flying long-haul, four hours or more," said Tiffany Pham, D.O., an OB-GYN in Houston and a medical advisor at women's health app Flo.

The likelihood of VTE is highest during flights that last 12 to 16 hours or more, according to the Centers for Disease Control and Prevention (CDC). Even so, the occurrences are low.

"Research shows that DVTs occurred in 3 out of every 1,000 people who flew flights of a duration of more than 4 hours," she said. "When compared to the DVT rate for people who did not fly, DVTs occurred in 1 out of every 1,000 people."

For additional perspective, the average international traveler is about 100 times more likely to die in a car crash than from a pulmonary embolism, according to a 2003 Australian study published in the journal BMJ Open.

Even frequent travelers who fly internationally every two weeks are more likely to die on the roads than in the air.

Why do long flights sometimes cause deep vein thrombosis?

"The main reason air travel—or taking a long bus, car or train ride—can increase the chances of VTE is that long periods of immobility can cause blood to pool in the lower legs and ankles, causing swelling," Pham said.

Additionally, having the backs of your knees pressed against the seat can compress the veins and inhibit blood circulation.

"When these two conditions occur simultaneously, there can be swelling of your lower legs as certain components within your blood vessel can leak out into the surrounding tissue. This causes the blood remaining inside the blood vessel to become thicker and more viscous," Pham said.

Thick, viscous blood and stagnant blood flow in the lower legs can combine to create blood clots.

"If you develop leg swelling on or after a flight that's not going away or is only on one side, see a doctor or your medical provider urgently, as this could be a symptom of a blood clot," Pham said.

Taking the combined pill is one of several factors that can raise your risk of developing a blood clot. People with other risk factors, such as pregnancy, clotting disorders or a family history of blood clots, are much more vulnerable, said Alexandra Kharazi, M.D., a cardiothoracic surgeon at Southern California Surgical in Chula Vista, California.

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What are the signs of deep vein thrombosis?

As many as 30 percent of people who develop DVT don't experience any symptoms of it, according to Cleveland Clinic. When symptoms do occur, they can be mild.

Sometimes, the clot dissolves on its own.

However, a blood clot can permanently damage the vein and its valves, increasing the likelihood of another clot, according to the National Blood Clot Alliance. Between 5 percent and 30 percent of people with DVT have a second episode within five years of the first.

A pulmonary embolism or stroke can occur if the clot breaks off and travels to the lungs or brain.

Know the silent signs of DVT. Symptoms of DVT may include the following, per Cleveland Clinic and Mayo Clinic:

Belly or flank pain (if the clots impact the veins in your abdomen)
Severe headache or seizures (if the clot affects the veins in your brain)
Pain, cramping or tenderness in the affected area can occur when you stand or walk
Skin that appears red or purple or feels unusually warm
Swelling in your leg or arm
Veins near your skin's surface that appear unusually large

If the clot travels to the lungs and causes a pulmonary embolism, symptoms can include:

Chest pain or discomfort
Coughing up blood
Fainting
Lightheadedness
Rapid pulse
Shortness of breath

How do you diagnose deep vein thrombosis or a pulmonary embolism?

A healthcare provider can diagnose DVT or PE by performing a physical exam and administering tests, which may include:

Computed tomographic angiography (CTA) scan. This test, primarily for diagnosing PE, uses contrast dye to provide a clear picture of the blood vessels in the chest.
D-dimer blood test. This test checks for D dimer, a protein that blood clots produce. Levels are usually higher in people with DVT or PE.
Duplex ultrasound. Sound waves show how blood flows through the veins. It's part of the standard protocol for diagnosing or ruling out DVT.
Magnetic resonance imaging (MRI). If a doctor believes you may have DVT in your abdomen, they may use this scan to get a picture of your veins.
Venography. Although rarely performed, this test uses X-rays and dye to get a clear look at the blood vessels of the legs and feet.

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Who is at a higher risk for blood clots while traveling?

People with a personal or family history of blood clots are more likely to have DVT in general, Kharazi noted. So are those with genetic clotting disorders, such as Factor V Leiden deficiency.

The following can also raise your risk of developing blood clots, according to the CDC:

Age 40 or older
Current or recent cancer
Hormone replacement therapy (HRT)
Limited mobility (such as a leg cast)
Overweight or obesity
Pregnancy
Recent injury or surgery
Smoking
Taking estrogen-containing contraceptives
Varicose veins

People with additional risk factors are usually advised against taking combined hormonal contraceptives because of their effect on blood coagulation, Pham said. Specifically, estrogen—found in combined oral contraceptive pills, patches and vaginal rings—drives the liver to produce more of certain clotting factors. While these help prevent high-volume blood loss from injury or childbirth, having more than necessary can increase the risk of VTE.

"Unless you have an underlying condition that affects blood clotting, the chances of developing DVT from hormonal contraceptives are slim," Pham said. "The potential risk of blood clots associated with certain forms of birth control should not scare you away from using these medications, as the overall risk is quite low."

Blood clots affect about 2 in 10,000 people who don't take hormonal birth control and 5 to 10 in 10,000 people who do, she said. For perspective, the risk of blood clots is much higher in pregnancy—20 out of 10,000 people.

"Therefore, if you avoid contraception because you're concerned about the risk of blood clots while on these medications, you run the risk of getting pregnant, which confers a higher risk of blood clots in general," she added.

If you're wary of using combined hormonal methods, progestin-only contraceptives—such as the mini pill or progestin-only implant—and nonhormonal IUDs don't carry the same VTE risk and may be a better option.

What are the dangers of flying with swollen legs?

"Swollen legs may signal a pre-existing condition such as heart failure, reduced mobility or chronic venous insufficiency that could make you more vulnerable to DVT," Kharazi said.

The latter occurs when the valves of the leg veins become weak and struggle to push blood back into the heart.

If you have swelling, talk to your doctor before heading to the airport to ensure you don't already have a blood clot or another serious issue that could make you prone to one.

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Can taking aspirin before a flight help prevent deep vein thrombosis?

Aspirin won't prevent blood clots during air travel, according to the CDC.

"Aspirin does keep platelets from sticking together, but this is only part of the coagulation cascade that causes blood clots," said Pamela Lee, F.N.P., a family nurse practitioner at White Wilson Medical Center in DeFuniak Springs, Florida.

Some people can benefit from taking aspirin for other purposes, such as heart attack or stroke prevention, according to Cleveland Clinic. But talk to your doctor because it can have adverse side effects and isn't suitable for everyone.

Should you wear compression socks while traveling if you have the risk factors for DVT?

"Compression socks may help to prevent DVT by improving circulation in the legs and reducing swelling," Lee said.

She suggested you put them on before you leave the house. And make sure they fit because they could restrict blood flow and be counterproductive if they're too long or bunch up.

"Generally speaking, they are a good idea to wear before long flights, but once again, check with your doctor," Kharazi said. "In certain conditions such as peripheral arterial disease, it may actually be harmful to wear these."

Pham listed other steps you can take to reduce the risk of swelling, including the following:

Consider booking an aisle seat to make it easier to move around.
Drink plenty of fluids to stay hydrated.
Put all of your bags in the overhead locker so you have more legroom under the seat in front of you.
Stand up and move every one to two hours during the journey.
Stretch your calf muscles by flexing your ankles toward the ceiling.

The bottom line

Although the risk is small, taking estrogen-containing contraceptives, coupled with sitting for a period of time, could increase your chances of developing deep vein thrombosis.

If you take the combination pill or have other risk factors, moving around and wearing compression socks may help prevent blood clots during your journey. If your ankles or legs are already swollen, talk to your doctor to ensure it's safe before heading to the airport.