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Deep vein thrombosis (DVT): What is the risk of developing DVT during a flight?

Created: ; Last Update: January 17, 2013.

Photo of airplane
The risk of DVT is very low for healthy travelers. Even for people with risk factors, there is little risk on flights less than four to six hours, although their risk is a little higher for long-distance flights. Compression stockings can reduce the risk.

Deep vein thrombosis (DVT) occurs when a blood clot forms in a person’s veins. Sometimes this causes symptoms such as tenderness, skin redness, swelling of the lower legs, or warmth around the affected area. But DVTs often cause no symptoms at all.

You can find more information on deep vein thrombosis (DVT) here.

Most DVTs go away without treatment and do not cause any problems. However, a deep vein thrombosis can be dangerous if the blood clot dislodges from where it has formed and moves on to the lungs, where it might block a blood vessel. This complication, called pulmonary embolism, can cause shortness of breath and may become dangerous very suddenly. It is most likely to happen within two weeks of a DVT developing.

Research on the risk of thrombosis during a flight

Two research groups, one from the University of Virginia in the United States, and the other from Leiden University in the Netherlands, searched for studies on deep vein thrombosis and flying (often called “economy class syndrome”). They found and analyzed studies covering the experiences of millions of air travelers. The results the researchers produced indicate that after a long-distance flight (longer than six to eight hours) around 2 to 5 10,000 travelers develop a DVT that causes symptoms. This means that these passengers have about the same chance of developing DVT as people who have to stay in bed for three days or who have varicose veins. For people flying less than four to six hours there was no increased risk of DVT from flying. This means that the risk of DVT for people flying longer than six to eight hours is about the same as for a person who is bedridden for three days or someone who has varicose veins.

The Dutch research group also addressed the question of whether longer trips increase the risk of DVT more. They found that the risk increases when a trip is longer than twelve hours, and that it keeps increasing a little as a trip gets longer. None of the studies looked at whether or not DVT is more likely in people who fly economy class than it is in those who fly business class.

Who is at a higher risk and how can DVT be prevented?

There are some medical conditions that can increase people’s risk of DVT when they fly. According to the U.S. researchers, it is only slightly higher for people who are more at risk: it is less than 0.2%, meaning that fewer than 20 out of every 10,000 people will be affected. The passengers shown to be at higher risk in these studies were people who had had a DVT before, were severely overweight, had limited mobility, or who had a blood clotting disorder, recent surgery, cancer or large varicose veins. People who have a leg in a cast or splint are also at higher risk of developing DVT.

The U.S. researchers found that putting on knee-high compression stockings at least two hours before the flight and wearing them during the entire flight can decrease the risk of DVT. ASA (acetylsalicylic acid, e.g. in “Aspirin”) has not been proven to prevent the risk of DVT for air travelers. Anticoagulant drugs such as heparin and warfarin have been shown to reduce the risk of thrombosis in other studies not involving air travel. But these drugs are more likely to cause heavy bleeding than ASA. What is more, it takes a few days for warfarin to start working, so it does not seem to be well-suited for preventing air-travel-related DVT.

The U.S. researchers stressed that for most people at low risk of DVT drinking plenty of fluids as well as exercising their leg muscles and walking around as frequently as possible during the flight are probably enough to avoid DVT.

In August 2012 we checked for new research results on deep vein thrombosis during flights but found no new systematic reviews. Other sources also do not indicate that any new research results are available. We therefore believe that this information reflects the current state of scientific knowledge on this topic.

You can read more about DVT in immobilized legs in our research summary “Can medication prevent thrombosis in immobilized legs?”

Published by the Institute for Quality and Efficiency in Health Care (IQWiG)
Next planned update: January 2016. You can find out more about how our health information is updated in our text "Informed Health Online: How our information is produced."


  • IQWiG health information is based on research in the international literature. We identify the most scientifically reliable knowledge currently available, particularly what are known as “systematic reviews.” These summarize and analyze the results of scientific research on the benefits and harms of treatments and other health care interventions. This helps medical professionals and people who are affected by the medical condition to weigh up the pros and cons. You can read more about systematic reviews and why these can provide the most trustworthy evidence about the state of knowledge in our information “Evidence-based medicine.” We also have our health information reviewed to ensure medical and scientific accuracy.
  • Kuipers S, Schreijer AJ, Cannegieter SC, Büller HR et al. Travel and venous thrombosis: a systematic review. J Intern Med 2007; 262: 615-634. [PubMed: 18028182]
  • Philbrick JT, Shumate R, Siadaty MS, Becker DM. Air travel and venous thromboembolism: a systematic review. J Gen Int Med 2007; 22: 107-114. [PMC free article: PMC1824715] [PubMed: 17351849]
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