We are going to Peru and Chile for a holiday but my wife is worried at the thought of getting altitude sickness as she suffers from terrible migraines. Is there anything we can do to reduce the possibility - the travel agent told me to drink the tea! Denis Michelson, by email

Sunday Times travel expert Richard Green responds: Altitude sickness is caused by the decreasing levels of oxygen in the air at higher altitudes. It can be a very serious illness, which in its worst case can prove fatal, but with the right precautions you should be fine; even if you are a migraine sufferer, as there isn't a proven link between migraines and suffering from altitude sickness.

The basic thing to remember is to take your time when going to higher altitudes, especially over 8,000ft. Most cases of altitude sickness come about by people not taking enough time for their bodies to adjust.

You should consult your GP before heading off on your South American adventure, as there are some treatments for altitude sickness that you can be prescribed. However it is important not to take them until you have symptoms - otherwise you could mask something important. Symptoms to look out for include headaches, nausea, vomiting, dizziness, malaise, insomnia, and loss of appetite.

It may sound a bit silly to recommend the local tea, but in fact your travel agent is on the right track there. Throughout South America there are derivatives of a tea called Mate, which has a weak derivative of cocaine in it, which locals say helps to prevent altitude sickness.

Incidentally, Tibetans or Bolivians coming down to the beach don't get low altitude sickness. It only is a problem for us low altitude dwellers going up.

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