High altitude: recognise altitude illness and descend

At every altitude, air is roughly one fifth oxygen. What changes is the air pressure: up high, less air weighs down on you, so the molecules are spread further apart. Each breath contains fewer oxygen molecules, and the blood in the lungs picks up less oxygen.

The body reacts immediately by breathing faster and deeper and by making the heart beat faster. Over days, further adjustments follow in the blood and metabolism – this process is called acclimatisation. How quickly it succeeds differs from person to person and can hardly be predicted beforehand. People who had problems on an earlier trip should expect that they may occur again.

The most common form is acute mountain sickness, with headache, nausea, loss of appetite, fatigue, dizziness or poor sleep. Rarer but life-threatening are high-altitude pulmonary oedema, in which fluid collects in the lungs, and high-altitude cerebral oedema, in which the brain swells. Altitude illness can occur from about 2,500 metres, in some people even lower.

The most important protection is time. The Wilderness Medical Society recommends that above about 3,000 metres you should raise your sleeping altitude by no more than about 500 metres per day, with a rest day every three to four days. What counts is the altitude where you sleep – going a little higher by day and descending again to sleep is a well-known principle.

Build these days into your plan from the start, with extra buffer. Fixed itineraries, booked accommodation and group pressure are common reasons why people carry on despite symptoms. Arriving by plane or car directly at high altitude is especially tricky, because the body has had no time to adjust.

Get medical or travel-medicine advice before the trip, especially if you have existing conditions. Medicines for prevention or treatment exist, but they belong solely in a doctor's hands – this text deliberately names no drugs and no doses.

A headache after an ascent, together with nausea, fatigue, dizziness or poor sleep, should be treated as possible altitude illness – not dismissed as „just a cold“. With such symptoms you do not climb further, you rest and tell your companions. If they do not improve or get worse, you descend.

Breathlessness at rest, confusion, unsteady walking or increasing drowsiness are emergencies. Then descend or be evacuated immediately and call for help – via the local emergency number (112 in the EU) or mountain rescue. An ill person never descends alone, because their condition can worsen on the way.

In a group, look out for one another. People who develop altitude illness often notice it poorly themselves or do not want to hold anyone up. Children sometimes cannot describe their symptoms well; if they are unusually whiny, listless or off their food, take it seriously.

At high altitude UV radiation is stronger, and snow reflects the light as well. Sunglasses, sunscreen and covering clothing protect eyes and skin. At the same time it is often cold and windy, and the weather can change quickly.

The air is dry and you breathe more – losing moisture with every breath. So drink safe water regularly. Because water boils at a lower temperature at altitude, cooking takes longer and you need more fuel.

A widespread misconception is: if you are fit, you will not get altitude sickness. Fitness helps with walking but offers little protection against altitude illness. Very fit people sometimes even ascend too fast, because they physically can.

The good news: a slow ascent prevents many cases, and descent almost always helps. If you plan your trip so that turning back is possible at any time and no deadline forces you onwards, you already carry the most important tool.