Avoid smoking or over eating. Choose a flight which arrives in the evening so you can sleep at a normal time. Much has been written in the press about blood clots linked to cramped seating on long haul flights, so-called 'Economy Class Syndrome'. Limited leg room and reduced movement for long periods can cause the circulation to slow down or stop altogether. Drink plenty of water.
Dehydration can trigger the effects by making the blood thick and sticky.
Much depends on the strength of the UV radiation and your natural skin colour. The World health Organisation has developed a way to advise people about the strength of the sun's rays and works on a scale of 1 to 20. You will often hear this referred to on weather forcasts as the 'UV Index'. According to new research there has been an alarming rise in the incidents of skin cancer among UK travellers and it can be directly linked to the fashion for exposing more of the skin to the sun. In the UK the UV Index is unlikely to get above 8.