Mal des montagnes

If you ascend too quickly to high altitude without acclimatising, you can get altitude sickness. The body then does not have enough time to adapt to the low oxygen level in the air.

This usually happens only above 2,500 metres. Whether you get altitude sickness varies by person and is not related to how fit you are. If you have had it before, you are more likely to get it again.

There are two forms: mild and severe.

• The mild form starts a few hours or a day after you arrive at high altitude. You are short of breath, have a headache, feel nauseous and may vomit. You feel dizzy and weak. Symptoms usually last a few days, but can progress to the severe form.
• In the severe form, headache and shortness of breath get worse, including at rest and especially at night. You can become so weak that you need help dressing and eating. Walking may look as if you are drunk. Without treatment you can develop fluid in the lungs and brain, fall into a coma and die.

You can lower the risk:

• Ascend slowly above 2,500 metres.
• Give your body two days to acclimatise when going higher than 2,500 metres.
• Do not use alcohol or sleeping pills.
• Preferably do not sleep more than 300 metres higher than the night before.
• In consultation with a doctor you can use acetazolamide if you have had altitude sickness before, or if you must ascend suddenly to a sleeping altitude above 3,500 metres without time to acclimatise.

For the mild form: do not go higher, or descend, if you are not better within a few days or if it gets worse. Paracetamol can help a headache. For the severe form, descend immediately. That can save your life. A clinician can give medicine or oxygen.