Deep Vein Thrombosis (DVT) is the formation of a blood clot in a deep vein, usually in the thigh or calf. DVT becomes dangerous if the blood clot breaks loose, travels in the bloodstream and lodges in an artery of the lung. The resultant serious condition is called Pulmonary Embolism.

Sitting in cramped seats in the same position for long periods of time, such as with long haul flights (long-distance bus or car travel can also bring on DVT) increases the risk of this condition, particularly for some individuals with pre-existing risk factors, such as:

• Increasing age (>40 years)
• Pregnancy
• Oestrogen hormone therapy, including oral contraceptives and hormone replacement therapy
• Smoking
• Obesity
• Former or current malignant disease
• Personal or family history of DVT
• Blood disorders leading to increased clotting tendency
• Recent major surgery or injury, especially to the lower limbs or abdomen
• Heart failure
• Varicose veins

Medication such as Heparin and graduated support stockings may be advisable for high-risk travellers and should be prescribed by a physician.