It has been known for many years that sitting or lying still for long periods of time can lead to the formation of blood clots in the deep-lying veins (usually those in the legs). This is known as deep vein thrombosis or DVT. More recently is has also been recognised that conditions inside an aeroplane on long-haul flights can increase the risk of deep vein thrombosis. This is where the terms travellers' thrombosis, flight-related DVT and economy class syndrome come from.Symptoms of traveller's thrombosis include pain, swelling or tenderness of the calves or thighs; an increase in skin temperature around the affected site; reddening of the skin or blue-red discolouration of the skin.

Deep vein thrombosis is not usually dangerous in itself but a blood clot or part of a clot can break away from the wall of the vein and travel around the body in the bloodstream. The clot can then get lodged in an artery, most commonly in the lungs, and cause a blockage which is known as an embolism. A blockage forming in the lungs can cause severe illness and can even be fatal. Symptoms include chest pain, shortness of breath and coughing up blood.


The heart pumps oxygenated blood around the body in the arteries. When the oxygen has been delivered to where it is needed, the veins then carry deoxygenated blood back to the heart. Blood that has circulated to the legs and feet has to work against gravity to get back to the heart so it relies on the normal muscular movement of the legs to act as a pump. During long periods of inactivity, the muscles in the legs do not flex as normal so blood does not flow as freely. This can lead to the formation of blood clots in the veins.During long journeys in an aeroplane, car, coach or train, seating conditions are usually cramped. Sitting still for prolonged periods of time, insufficient legroom, squashing the leg veins against the edge of a seat and sleeping in a sitting position can all prevent blood circulating properly which can increase the risk of deep vein thrombosis.The dry atmosphere inside an aeroplane and drinking alcoholic drinks can cause dehydration. This can affect fluid levels in the body and can make blood thicker and more likely to clot.

Low oxygen levels and reduced air pressure in the cabin can widen the veins in the legs which slows down the flow of blood. This can cause the legs and feet to become swollen which slows down blood flow even more, increasing the risk of a blood clot.

Risk Factors

You may be more at risk from travellers' thrombosis if you are pregnant or have just had a baby, if you are overweight, if you are over 6ft tall or under 5ft tall (height can affect your seating position), if you are over 40 years of age, if you have a history of thrombosis, if you have severe varicose veins, if you are a woman taking a contraceptive pill or hormone replacement therapy (HRT), if you have recently had surgery (especially surgery involving the lower leg), if you have recently injured one of your legs, if you have any blood clotting disorders, if you have recently suffered a stroke, if you smoke, if you have cancer, if you are having radiotherapy treatment, if you have heart disease or if you are paralysed.

Avoiding Travellers' Thrombosis

  • If possible, before leaving for the airport, take some form of exercise such as walking, running or swimming. While you are waiting for your flight to be called, walk around the airport
  • Wear loose fitting clothes and undergarments
  • Wear compression socks. Below the knee socks are available especially for flying. They apply gentle pressure to the ankle which improves blood flow by squeezing it upwards
  • If you are susceptible to deep vein thrombosis, request an aisle seat or one with extra leg room
  • If you are going on a long-haul flight, consider an overnight stopover to break your journey
  • In low doses, aspirin can prevent the formation of blood clots by stopping tiny cells in the blood (platelets) clumping together to form clots. Taking half a 300mg tablet two hours before your journey may help to prevent travellers' thrombosis (one dose is sufficient for any length of journey). Some people should not take aspirin so ask your pharmacist or doctor to advise yo
  • If you are particularly at risk from travellers' thrombosis, your doctor may decide to give you a heparin injection or some oral anticoagulants (blood thinners) which are both used to prevent the formation of blood clots
  • During your journey, do not sit in the same position for too long. If possible, stretch your legs once every hour by walking around
  • When you are sitting down, do some simple exercises every half hour. Try a combination of the following: circle your ankles; rock your feet on to your heels and the balls of your feet alternately; lift your knees so that your thighs lift from the seat and your feet lift off the floor; roll your neck and shoulders; touch your toes; hug your knees into your chest one at a time
  • Exercise cushions are available which are specially designed to help you exercise your arms and legs on long journeys. Ask your pharmacist for more information
  • Do not cross your legs or ankles
  • Only use a foot rest if it supports the whole of your lower leg. Do not use it if it presses on your leg or if your feet or calves are dangling off the end.ยท Try not to sleep in an uncomfortable position
  • If you take sleeping tablets you will be less likely to move around during your sleep so do not take them before or during your flight
  • Drink plenty of water or soft drinks during your journey (try to drink two small glasses every hour). Alcohol has a diuretic effect which means that it makes you lose fluid by increasing your urine output. You should therefore avoid alcohol while you are flying to prevent further loss of fluid. Drinks containing caffeine such as tea and coffee also have a mild diuretic effect. However, as long as you drink them regularly and at normal strengths, these drinks will still contribute to your water intake. You should also avoid salty snacks during your journey
  • Take regular deep breaths to increase your oxygen intake
  • Give up smoking


Small clots often break up on their own but anticoagulants (blood thinners) can be used to prevent the clot becoming any bigger. Thrombolytic medicines may also be used to break up blood clots. If there is a danger that the clot may dislodge, it can be removed using surgery. Tests and treatment for deep vein thrombosis are carried out in hospital.

When To See A Doctor

If a blood clot forms during a journey, part of the clot could break away and travel to your lungs two weeks or more after you have travelled. If you have recently been on a long journey and you develop any of the following symptoms, tell your doctor immediately: pain or swelling of the calves or thighs, tenderness, an increase in skin temperature around the affected site, redness or blue-red discolouration of the skin, a high temperature, chest pain, shortness of breath or coughing up blood.

Additional Information

Leaflets about other travel health issues are also available from any pharmacy.