Prevention for deep vein thrombosis (DVT) comes down to a few habits: keep your blood moving, avoid long periods of sitting or lying still, stay hydrated, keep a healthy weight and do not smoke. A DVT is a blood clot in a deep vein, usually in the leg, and it can sometimes travel to the lungs. You cannot remove all risk, because some triggers such as surgery, cancer or pregnancy are outside your control, but there is a lot you can do to tilt the odds in your favour. This page covers everyday prevention, what to do on long flights and what to know in hospital.
How blood clots form, in brief
Clots tend to form when blood flow slows, when the lining of a vein is damaged, or when the blood clots more easily than usual. Most prevention advice targets the first factor. Your calf muscles act like a pump: each time they contract, they squeeze blood up the deep veins towards the heart. When you are still for hours, that pump switches off and blood can pool.
DVT is treatable, but it is best avoided where possible, because a clot can lead to a pulmonary embolism. You can read about that complication on our page on pulmonary embolism.
How to reduce deep vein thrombosis risk day to day
The following habits are supported by NHS and NICE advice and are low-risk for most people.
- Move regularly. Walk, stretch or change position often. If you have a desk job, stand up and walk around from time to time rather than sitting for hours.
- Keep a healthy weight. Excess weight raises clot risk. Gradual, sustainable weight management is better than crash diets.
- Do not smoke. Smoking affects blood vessels and clotting.
- Stay hydrated. Drinking enough fluids is sensible, especially in hot weather and when travelling, although water alone will not prevent a clot.
- Stay active after illness or surgery. Getting up and walking as soon as your care team says it is safe is one of the most effective protections.
- Know your risk factors. Cancer, a previous clot, a family history of clots, pregnancy and the weeks after birth, and oestrogen-containing medicines all raise risk. If any apply to you, ask your doctor about a personal plan.
Many people with varicose veins wonder whether their veins raise clot risk. Varicose veins and DVT are different problems, although they can occur together. If you want to know more about your own legs, our vein check helps you decide what to ask a doctor.
Deep vein thrombosis and flights
A common worry is deep vein thrombosis on flights. Sitting in a confined space for many hours slows blood flow in the legs, and long-haul travel is associated with a modest increase in clot risk. The risk is generally small for healthy travellers and tends to be higher when other factors stack up, such as recent surgery, cancer, pregnancy, obesity or a past clot. Long car, bus or train journeys carry a similar effect because the cause is immobility, not the aircraft itself.
What helps on a long flight
If you are on a DVT long flight, these steps are widely recommended:
- Walk up and down the aisle when it is safe and the seatbelt sign is off.
- Do seated calf exercises: raise and lower your heels, then your toes, and rotate your ankles regularly.
- Avoid sitting with your legs tightly crossed or wedged under the seat for long periods.
- Choose an aisle seat if you can, so it is easier to stand and stretch.
- Drink fluids and go easy on alcohol, which can lead to dehydration and deeper sleep with less movement.
- Avoid tight clothing around the waist, thighs or knees.
Some travellers with higher risk may be advised by their doctor to wear graduated compression stockings or to use other preventive measures. This is an individual decision. For general information on stockings, see our compression stockings guide, and speak to your doctor before relying on them for clot prevention.
How long after a flight can DVT occur?
Clots linked to travel do not always appear during the trip. Symptoms can begin within days and, in some cases, up to a few weeks later. So if you notice swelling, pain, warmth or colour change in one leg after a long journey, do not dismiss it just because you have landed. If you want more detail, the question of how long after a flight DVT can occur is covered by specialists who treat clots.
Prevention in hospital and after surgery
Being in hospital is one of the most common triggers for DVT, because illness and bed rest reduce movement and surgery can affect clotting. In hospitals following NICE guidance, staff assess each patient’s risk on admission. Depending on your risk, you may be offered compression devices, encouraged to walk early, or offered preventive treatment. If you are not sure what has been arranged for you, ask.
At home after discharge, follow instructions about activity and any treatment you have been prescribed. Do not stop or change prescribed medicines without talking to your doctor.
Pregnancy, hormones and other special situations
Pregnancy and the weeks after birth raise clot risk, and so can some hormone-containing medicines. These are not reasons to avoid treatment or contraception on your own. They are reasons to tell your doctor about any personal or family history of clots so your risk can be weighed properly.
Related pages
If you are worried about leg symptoms, these pages may help you tell the difference between common causes:
- Swelling in one leg explains why one-sided swelling needs attention.
- Leg swelling covers common causes and when it is dangerous.
- Can you dissolve blood clots naturally? looks at remedies that are often claimed online.
Warning signs of a clot
Knowing the signs matters as much as prevention. DVT often affects one leg and can cause swelling, aching or tenderness, warmth, redness or a darker colour. Some people have no symptoms at all. A clot that reaches the lungs can cause sudden shortness of breath, chest pain or coughing blood.
When to see a doctor
See a doctor promptly, the same day if possible, if you have a swollen, painful, warm or discoloured leg, especially on one side, or if you developed these signs after a long journey, surgery or illness. Do not massage the leg or wait to see if it settles.
Call 995 immediately if you have sudden chest pain, sudden breathlessness or you cough up blood, as these may be signs of a clot in the lungs. This is an emergency.
If you have a past clot, cancer, or other risk factors and are planning a long trip, book a check-up before you travel to discuss a plan that suits you.
This page is general education and not a substitute for personal medical advice.
Frequently asked questions
How can I reduce my risk of deep vein thrombosis every day?
Stay active, avoid sitting or lying still for long stretches, keep a healthy weight, do not smoke and drink enough fluids. If you have extra risk factors, such as recent surgery, cancer or a past clot, ask your doctor what is right for you.
Are long flights dangerous for DVT?
Long journeys of roughly four hours or more raise the risk of a clot a little, mainly because you sit still for a long time. Most travellers never have a problem. The risk matters more if you also have other risk factors.
How long after a flight can DVT occur?
Symptoms can start during a trip, but clots can also show up days or even a few weeks afterwards. Any new one-sided leg swelling or pain after a long journey should be checked promptly.
Do I need to take medicine before a flight to prevent DVT?
Most people do not. Whether preventive treatment is suitable depends on your personal risk, so this is a decision to make with your doctor before you travel, not something to start on your own.
Do I need to see a doctor before a long trip?
It is worth a conversation if you have had a clot before, have cancer, are pregnant or recently gave birth, recently had surgery, or take hormone-containing medicines.
Sources and further reading
This article is general information, not personal medical advice. Please speak to a doctor about your own symptoms. How we create our content.
