Mountain climbers are at risk of developing altitude sickness (also known as mountain sickness), which may be harmful or even fatal if its onset is ignored. It is caused by gaining altitude too rapidly, which doesn't allow the body enough time to adjust to reduced oxygen and changes in air pressure, and causes hypobaric hypoxia (a lack of oxygen reaching the tissues of the body).

In severe cases, fluid builds up within the lungs, brain or both. At intermediate altitude (1,500 to 2,500 metres above sea level) altitude illness is unlikely, though possible. Acute altitude sickness arises after at least four hours spent at an altitude above 2,000 m. Ascending to heights greater than 2,500 m can trigger a range of symptoms including headache and vomiting.

Men are at greater risk of altitude sickness than women, for reasons unknown. It is important to remember that being young and fit doesn't reduce your risk, and just because you haven't experienced altitude sickness in the past, doesn't mean you are immune to the condition during future climbs. The only sure method of prevention is to take plenty of time to ascend.

Symptoms of altitude sickness

The initial symptoms of altitude sickness can include:

Headache

Lethargy

A drop in performance

Lack of coordination

Insomnia

Appetite loss

Dizziness

Nausea

Vomiting.

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