Deep Vein Thrombosis - Prevention When Travelling

This leaflet advises on how to reduce the risk of a deep vein thrombosis occurring during a long journey. Another leaflet discusses deep vein thrombosis in more detail.

What is a deep vein thrombosis?

A deep vein thrombosis (DVT) is a blood clot that forms in a deep leg vein. The deep veins are blood vessels which go through the calf and thigh muscles, and are not those which you can see just below the skin.

Is a deep vein thrombosis serious?

It can be. When a blood clot forms in a leg vein it usually remains stuck to the vein wall. The symptoms tend to settle gradually, but there are two main possible complications:

  • Pulmonary embolus (a blood clot in the lung) occurs in a small number of people who have a DVT. An embolus is a part of a blood clot which breaks off and travels in the bloodstream. An embolus that comes from a clot in a leg vein will be carried up the larger leg veins to the heart, through the large heart chambers, but will get stuck in a blood vessel going to a lung (pulmonary embolus). This is serious, and can sometimes be fatal.
  • Long-term discomfort and swelling of the calf occur in some cases following a DVT (post-thrombotic syndrome).

Who is at risk of having a deep vein thrombosis?

Anyone may develop a DVT, but the following increase the risk:

  • Immobility which causes blood flow in the veins to be slow. Slow flowing blood is more likely to clot than normal flowing blood.
    • A surgical operation which lasts more than 30 minutes is the most common cause of a DVT. The legs become still when you are under anaesthetic. Blood flow in the leg veins can become very slow.
    • Any illness or injury that causes immobility increases the risk of a DVT.
    • Long journeys by plane, train, etc, are thought to cause a slightly increased risk of DVT. This is probably due to sitting cramped for long periods.
  • Damage to the inside lining of the vein increases the risk of a blood clot forming. For example, a DVT may damage the lining of the vein. So, if you have a DVT, then you have a higher than average risk of having another one sometime in the future. Some conditions such as vasculitis (inflammation of the vein wall) and some drugs (for example, some chemotherapy drugs) can damage the vein and increase the risk of having a DVT.
  • Conditions that cause the blood to clot more easily than normal (thrombophilia) can increase the risk of having a DVT. Some medical conditions can cause the blood to clot more easily than usual. For example, nephrotic syndrome and antiphospholipid syndrome. Some rare inherited conditions can also cause the blood to clot more easily than normal. For example, factor V Leiden.
  • The contraceptive pill and hormone replacement therapy (HRT) which contain oestrogen can cause the blood to clot slightly more easily. Women taking 'the pill' or 'HRT' have a small increased risk of DVT.
  • People with cancer or heart failure have an increased risk of having a DVT.
  • Older people are more likely to have a DVT, particularly if you have poor mobility or have a serious illness such as cancer.
  • Pregnancy increases the risk. About 1 in 1000 pregnant women have a DVT.
  • Obesity also increases the risk of having a DVT.

What is travel-related deep vein thrombosis?

Long journeys (more than four hours) by plane, train, etc, are thought to cause a slightly increased risk of DVT. This is probably due to sitting immobile and cramped for long periods. In plane journeys, in addition to the immobility, other factors which may possibly play a part (but are not proven) include: the reduced cabin pressure, reduced oxygen levels in the plane, slight dehydration caused by not drinking much water, and drinking too many alcoholic drinks which are often freely available.

It has to be stressed that the vast majority of travellers have no problems. The increased risk of DVT from travel is small. Research studies suggest that there is about one DVT for every 6,000 journeys that last four hours or more. Also, it is difficult to rule out that the people who have a DVT after a journey would have had one anyway and the journey was a coincidence. (DVT is quite a common condition in the general population anyway.) Nevertheless, it is wise to try to reduce the risk, particularly if you are in any of the other 'at-risk' groups listed above.

How can I reduce the risk of travel-related deep vein thrombosis?

Whilst travelling on a long journey, particularly on a long-haul plane trip:

  • Exercise your calf and foot muscles regularly:
    • Every half hour or so, bend and straighten your legs, feet and toes when you are seated.
    • Press the balls of your feet down hard against the floor or foot-rest every so often. This helps to increase the blood flow in your legs.
    • Take a walk up and down the aisle every hour or so, when the aircraft crew say it is safe to do so.
    • If you are allowed, get off the plane and walk about if the plane stops for refuelling.
    • Consider buying a leg exerciser for the journey (see below).
  • Drink plenty of water (to avoid dehydration).
  • Do not drink too much alcohol. (Alcohol can cause dehydration and immobility.)
  • Do not take sleeping tablets, which cause immobility.
  • Consider wearing compression stockings (see below).
  • Some people at high risk may also be advised to take anticoagulant medication (see below).

Elastic compression stockings

There is some evidence to suggest that compression stockings can help to prevent travel-related DVT in people who have a high to moderate risk. You can buy the stockings from pharmacies. Ask the pharmacist for advice about the correct sort. They need to be 'graduated compression' stockings, worn to the knee, with the correct amount of compression (class 2). The slight pressure from the stocking helps to prevent blood 'pooling' in the calf. Stockings do not replace the need for regular exercises. They are in addition to exercises.

Anticoagulant medication

Some people at particularly high risk of DVT may be advised to have a heparin injection before a long-haul flight. Heparin is an anticoagulant (it 'thins the blood' and makes it less likely to clot). See your doctor before the journey to discuss this option if you:

  • Have had a previous DVT or pulmonary embolus.
  • Have a family history of clotting conditions.
  • Have cancer, or had treatment for cancer in the past.
  • Had major surgery in the last three months. In particular if you had a hip or knee replacement within the last three months. (Many doctors advise if you have had hip or knee replacements then you should not go on a long-haul flight for for at least three months after the operation.)
  • Have had a stroke.

Note: aspirin is not used to prevent DVT. (Aspirin is widely used to help prevent blood clots in arteries which can cause strokes and heart attacks. However, aspirin does not seem to be very effective at preventing clots in veins.)

Further research may clarify the value of compression stockings and heparin, or find other ways of preventing DVT.

After the journey

Have a little walk straight after the journey to 'get the circulation going'. The vast majority of travellers have no problems. However, if you develop a swollen painful calf or breathing difficulties shortly after a long journey, then see a doctor urgently. (But note: slight painless puffiness of feet and ankles is common after a long journey and is not due to a DVT.)

Further advice

Department of health advice

Regarding travel-related DVT - see their website

Health Advice to Travellers:

This booklet (T6) is available free from the Health Literature Line on 0800 555 777. It also contains an application for an E111 form, which is required for free medical treatment by UK citizens travelling in the EU. The information is also available on

Leg exercisers

A number of companies make devices which are designed to enable you to do leg exercises when seated on a plane. Some are listed on the DVT page on