Altitude sickness - also known as acute mountain sickness (AMS) - is a potentially life-threatening condition that can occur when a person is exposed to a high altitude without prior acclimatisation (the process of gradual exposure to high altitudes).
Altitude sickness occurs as a result of a decrease in atmospheric pressure which makes breathing difficult. Other common symptoms include:
- headache,
- nausea,
- dizziness, and
- exhaustion.
In severe cases, altitude sickness can cause pulmonary oedema (fluid on the lungs) and cerebral oedema (fluid on the brain). These are very serious complications that require immediate medical attention.
At what altitude does altitude sickness occur?
In its mildest form, altitude sickness can occur at about 2,500m (8,000ft) above sea level, which is a common height for many ski resorts. However, the more severe symptoms of altitude sickness occur at higher altitudes of 3,600m (about 12,000ft) and above.
How does altitude sickness occur?
As you climb higher up a mountain, the air that you breathe still contains the normal amount of oxygen (21%), but the atmospheric pressure decreases. This means that each breath that you take contains fewer molecules of oxygen.
For example, at 5,500m (18,000ft), each breath will contain roughly half the normal amount of oxygen (10.5%).
Who is affected by altitude sickness?
There are no specific factors, such as age, sex, or physical condition, that increase a person’s likelihood of getting altitude sickness. Some people are affected by altitude sickness, while others are not as susceptible to the condition.
However, most people are able to ascend to a height of 2,500m (8,000ft) without developing the symptoms of altitude sickness.
How common is altitude sickness?
Altitude sickness is a fairly common condition among people who spend time at high altitudes, such as mountaineers and skiers. For example, at a height of over 3,000m (10,000ft) approximately 75% of people will experience mild symptoms (see the ‘symptoms’ section).
Statistics also show that between 20-25% of people who go skiing in Colorado, and 53% of trekkers at Periche, which is en route to the Everest base camp, in Nepal, and is at an altitude of 4,240m (just under 14,000ft), will develop the symptoms of altitude sickness. Also, in the Swiss Alps, 34% of those who ascend to altitudes of 3,600m (about 12,000ft) or above, will experience some degree of altitude sickness.
It is not possible to get altitude sickness in the UK because the highest mountain is Ben Nevis, in Scotland, which is only 1,344m (4,406ft) high.
