Travel and Blood Clots: Who Is Actually at Risk, and What Helps

Travel-related clots are talked about far more than they occur, which leads to two errors: healthy travellers taking unnecessary medication, and genuinely high-risk travellers taking no precautions at all. The useful framing is that long journeys are a modest additional risk factor, and they matter most when stacked on top of others.

What raises risk on a long journey

Immobility is the main mechanism — prolonged sitting with the knees flexed slows venous return from the calf. Duration matters more than the mode of transport: long car, bus and train journeys carry the same principle as flights, and risk rises with journeys beyond roughly four hours.

Who should take it seriously

• Anyone with a previous DVT or pulmonary embolism.
• Recent surgery, particularly abdominal, pelvic or orthopaedic, or a recent lower-limb cast.
• Active cancer or ongoing cancer treatment.
• Pregnancy and the six weeks after delivery.
• Known thrombophilia, or a strong family history of clots at a young age.
• Combined hormonal contraception or hormone replacement therapy, especially with other factors present.
• Significant obesity, or reduced mobility for any reason.

A healthy person with none of these taking one long flight a year has a small absolute risk, and general measures are sufficient.

What actually helps

• Walk the aisle or stop the car roughly every two hours where it is practical.
• Do seated calf pumps — heel raises and ankle circles — every half hour; this is the single most useful in-seat measure.
• Keep well hydrated and avoid excess alcohol, which encourages sitting still and dehydration.
• Choose an aisle seat if that makes you more likely to get up.
• Avoid crossing the legs for long periods and avoid tight bands at the knee.

Compression stockings

Below-knee graduated compression stockings reduce leg swelling on long journeys and are reasonable for higher-risk travellers. Fit matters: a stocking that rolls down at the knee or bunches behind it is worse than none. They are a comfort and swelling measure for most travellers, not a substitute for medical prophylaxis in someone at genuinely high risk.

What not to do without advice

Do not take aspirin as clot prevention for travel on your own initiative — it is not the recommended approach for venous clots. Prophylactic anticoagulant injections are appropriate only for selected high-risk travellers and should be prescribed after an individual assessment, taking bleeding risk into account.

Symptoms in the days after travel

Most travel-related clots present within a couple of weeks of the journey, not during it. Watch for one-sided calf or thigh swelling, aching or tightness in the calf, warmth or discolouration, and — urgently — breathlessness or chest pain. Mention the journey when you present; it changes the clinical likelihood score.

If you have had a clot before

Plan the journey at a consultation rather than at the airport: your current medication, the reason for the previous clot and the journey length together determine whether stockings alone are enough or prophylaxis is warranted. That conversation takes one appointment and removes the guesswork.