Why does travel raise the risk?
When you sit for hours, the calf muscles do not work; because the calf muscle pump stops, blood in the leg slows down. The knees and groin stay bent, so the veins are also compressed. Slowed blood makes clot formation easier. This applies to planes and equally to sitting for a long time in a bus, car or train.
In a pooled analysis of studies, the risk of a clot was found to be about 3 times higher in travellers, and the risk rose the longer the journey lasted.
Each 2-hour increase in travel time raises the risk of a clot by about
0%
For air travel, this figure is 26% for every 2 hours.
Meta-analysis of observational studies; the increase in risk is relative, and for most travellers the absolute risk is low.
Chandra D et al. Meta-analysis: travel and risk for venous thromboembolism. Ann Intern Med 2009;151(3):180-190.
doi:10.7326/0003-4819-151-3-200908040-00129
Who should take extra care?
If any of the following applies and your journey is longer than 4 hours, talk to your doctor before you leave:
- A previous blood clot in the leg or a pulmonary embolism
- Surgery, a fracture or a cast within the last few weeks
- Active cancer treatment
- Pregnancy or the first weeks after childbirth
- Taking birth control pills or hormone therapy
- Older age, marked overweight or limited mobility
- An inherited clotting disorder
For people at risk, the doctor may recommend stockings or other measures depending on the length of the journey and the person's condition. Clot-preventing injections or medicines should be used only on a doctor's decision.
Take breaks, walk.
What to do on the way
- Get up and walk for a few minutes every 1-2 hours; take breaks on car journeys.
- Do ankle movements in your seat: pull your toes toward you and push them forward, and rise onto your toes. Have a look at the exercises.
- If possible, sit on the aisle side; do not cross your legs.
- Drink plenty of water; alcohol and sleeping pills may cause you to sleep without moving for a long time.
- Choose comfortable clothes that do not squeeze your legs.
Do compression stockings help?
In a Cochrane review of randomized trials on flights longer than 5 hours, people who wore below-knee compression stockings had markedly fewer symptomless leg clots and less leg swelling. It is important that the stockings fit properly; stockings that are too tight or that roll up may do more harm than good.
On long flights, symptomless clots were seen in 47 people who did not wear stockings, but in only
0people
who did. A total of 2,637 passengers were followed.
Review of 12 randomized trials; no symptomatic clot or pulmonary embolism was reported in the trials.
Clarke MJ et al. Compression stockings for preventing deep vein thrombosis in airline passengers. Cochrane Database Syst Rev 2021;4:CD004002.
doi:10.1002/14651858.CD004002.pub4
For choosing and putting on stockings, see the page How are compression stockings used?
Which symptoms need urgent attention?
If any of the following symptoms occur during the journey or in the days afterwards, seek care without delay:
- In one leg: sudden swelling, pain, warmth or redness: go to a healthcare facility the same day.
- Sudden shortness of breath, chest pain, bloody sputum or fainting: this may be a pulmonary embolism; go to the nearest emergency department immediately.
References
- Chandra D et al. Meta-analysis: travel and risk for venous thromboembolism. Ann Intern Med 2009;151(3):180-190. doi:10.7326/0003-4819-151-3-200908040-00129
- Clarke MJ et al. Compression stockings for preventing deep vein thrombosis in airline passengers. Cochrane Database Syst Rev 2021;4:CD004002. doi:10.1002/14651858.CD004002.pub4
This page is for information only; an examination is needed for diagnosis and treatment.
Related pages
Deep vein thrombosisBlood clot in the leg: symptoms and treatment
How are compression stockings used?Size, pressure and putting them on
Movement and exerciseLeg exercises you can do at home