Being immobile for a long time, such as during a long flight, can increase your risk of getting a blood clot. This can lead to life threatening complications. But you can do things to reduce the risk. With the right preparation, even people with a history of blood clots can enjoy air travel.

Blood clots occur when blood flow is slowed or stopped. Sitting still for extended periods of time can affect blood circulation and lead to the development of blood clots.

Airplane flights of four hours or more are a risk factor for deep vein thrombosis (DVT) and pulmonary embolism (PE). DVT and PE are serious complications of blood clots that may be fatal in some cases.

Read on to learn more about the connection between blood clots and flying and what you can do to reduce your risk.

In general, clotting is the typical function of the blood. But if it happens inside your blood vessels, it can limit the flow or cause a blockage. This is called thrombosis.

Your blood needs to move freely. Blood transports oxygen to the brain, so if there’s a full or partial blockage, your brain will not get what it needs to keep your body working as it should.

When this occurs in the vein, it is called venous thromboembolism (VTE). VTE includes DVT and PE. DVTs usually occur in the limbs.

A PE can happen when the blood clot travels to the lungs. It ultimately can prevent your heart from pumping blood, which leads to heart failure. Both DVY and PE are life threatening.

If you are flying long-distance, your risk of getting a blood clot during or shortly after the flight is about three times higher.

Being sedentary for a long time is one reason you might develop a blood clot due to a long flight. In addition, when you’re in an airplane, you’re sitting in an area with reduced air pressure. This causes you to take in less oxygen when you breathe.

This is known as hypoxia. This oxygen loss is mild in most cases. However, it can slow blood flow, increasing the risk of a blood clot forming. In some cases, the blood clot can progress to DVT or PE.

Your doctor will help determine if you should fly or if it makes sense to postpone your travel plans. Many factors will play into this decision, including:

  • your health history
  • the location and size of the clot
  • flight duration

Many other factors can increase your risk for blood clots. These factors can also increase your risk if you are on a long flight. These include:

  • personal history of blood clots
  • family history of blood clots
  • personal or family history of a genetic clotting disorder, such as factor V Leiden thrombophilia
  • being 40 or older
  • smoking cigarettes
  • having a body mass index (BMI) in the obese range
  • using estrogen-based contraception, such as birth control pills
  • taking hormone replacement medication (HRT)
  • having had a surgical procedure within the past three months
  • vein damage due to injury
  • current or recent pregnancy (six weeks post-delivery or recent loss of pregnancy)
  • having cancer or a history of cancer
  • having a vein catheter in a large vein
  • being in a leg cast

You can take several steps to help reduce your risk for blood clots while flying.

These include:

  • Take medication: Your doctor may recommend medical treatments to decrease your risk based on your health history. These include taking Aspirin or a blood thinner, either orally or via injection, 1-2 hours before flight time.
  • Wear compression socks: Wearing these can help promote better blood circulation in your legs while sitting in a plane. However, there are different types of compression socks, so make sure to pick the right ones for you and ask your doctor if you’re unsure.
  • Choose a spacious seat: If you can, select an aisle or bulkhead seat, or pay an additional fee for a seat with extra legroom. That will help you stretch out and move around during the flight.
  • Move around: Get up and walk around at least once an hour and exercise your calf muscles while seated. Do this by extending your legs straight and flexing your ankles upward. If you have enough space, bring your knee up to your chest, place your hands on your calf and hold for 10-15 seconds.
  • Communicate with the airline: If you know you are prone to blood clots, you may wish to alert the airline before the flight. That way, the crew will be more lenient in allowing you to move around the plane.
  • Massage your leg muscles: In addition to moving your legs, massage can help promote better circulation. Bring a tennis or lacrosse ball on board with you. While seated, gently push the ball into your thigh and roll it up and down your leg. Alternatively, you can place the ball under your leg and move your leg over the ball to massage the muscles.

According to the 2021 guidelines by the American Society of Hematology (ASH), preventive medication and wearing compression socks are remedies more appropriate if you know you are at a higher risk of developing a blood clot.

Other things you can do include:

  • Avoid crossing your legs, which can reduce blood circulation.
  • Wear loose, non-constricting clothing.
  • Stay hydrated by drinking at least 8 ounces (oz) of water an hour, and avoid or limit any beverage that can promote dehydration, such as alcohol or coffee.

Preventing blood clots during other forms of travel

Whether in the air or on the ground, long periods of time spent in a confined space may increase your risk of blood clots.

  • Plan scheduled breaks to stretch your legs or take short walks if you travel by car.
  • If you are on a bus or train, standing, stretching, and walking in the aisles can help. You can also walk in place at your seat if you have enough room, or take a few minutes in the lavatory to stretch your legs or walk in place.

Possible symptoms include:

  • leg pain, cramping, or tenderness
  • swelling in the ankle or leg, usually only on one leg
  • discolored, bluish, or reddish patch on the leg
  • skin that feels warmer to the touch than the rest of the leg

It’s possible to have a blood clot and not show any symptoms.

If your doctor suspects you have a DVT, you will be given diagnostic testing to confirm the diagnosis. Tests may include venous ultrasound, venography, or MR angiography.

Symptoms of a pulmonary embolism include:

  • shortness of breath
  • chest pain
  • coughing
  • dizziness
  • irregular heartbeat
  • sweating
  • swelling in the legs

PE symptoms are a medical emergency requiring immediate care. Your doctor may perform a CT scan to confirm the diagnosis before treatment.

Read on for answers to more questions about blood clots and flying.

Should you fly if you have a blood clot?

If you have a history of blood clots or have recently been treated for them, your risk of developing a PE or DVT while flying is even higher. It may not be a good idea to fly immediately, but you should consult your doctor to decide if it is safe.

Can you fly while on blood thinners?

Some medical professionals recommend waiting for four weeks after treatment with medications is complete before taking to the air.

How can you tell if a blood clot is moving?

The symptoms of a blood clot moving to the arteries in the lung can include heart palpitations, shortness of breath, chest pain, dizziness, and fever.

Does flying make blood clots worse?

A prolonged lack of movement increases the risk of a blood clot forming. In addition, the lower air pressure during flight also increases this risk. For this reason, the recommendation is if you’ve had a blood clot recently, you shouldn’t travel for at least 4 weeks. Blood-thinning medications used to treat DVT need time to help the clot break and reduce symptoms. In some cases, your doctor may want you to wait longer.

Long airplane flights may increase the risk for blood clots in some people, including people with additional risk factors, such as personal or family history of blood clots. Preventing blood clots during airplane travel and other forms of travel is possible. Understanding your personal risk and learning preventive steps you can take during traveling can help.

If you are currently being treated for a blood clot, or have recently completed treatment for one, talk with your doctor before boarding a flight. They may recommend delaying travel or offering medication to help reduce your risk for serious complications.