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What Is Altitude Sickness?

Mountain climbers camping high altitude

For most people, ascending to areas above 3000m is a wonderful experience. However, for some, the “thin” air causes problems. Around 1 in 100 people will start to feel unwell at 3000m with a condition called acute mountain sickness (AMS), which is often referred to as altitude sickness. At 4000m (often found in South America or the Himalayas), 50 in 100 people will initially have some uncomfortable symptoms.

Occasionally, serious complications occur. These can include brain swelling (HACE) and lung swelling (HAPE). Before you travel, make sure you know how to spot and treat these serious conditions.

Who gets ill?

This is difficult to predict and there are no hard and fast rules, except one: the quicker you ascend, the more likely it is that you will become unwell.

Above 3000m, you should ideally ascend no more than 1000m every 4 days. If this rule is adhered to, most people find that they are not badly affected by sickness. In some situations, however, a much faster ascent is unavoidable - for example, when flying to the Bolivian city of La Paz you are immediately at 3800m.

What will I feel like?

The most common symptoms of altitude sickness (AMS) are nausea, vomiting, tiredness, poor sleep and headache. These symptoms should settle as you spend more time at altitude - this is called acclimatisation.

In rare cases, people experience more pronounced symptoms. HACE results in severe headache, confusion, disorientation, unconsciousness and even death. HAPE results in shortness of breath at rest (this is different to feeling out of breath during exercise, which is common at altitude).

What should I do if I feel unwell?

For the mild symptoms of altitude sickness you should take simple painkillers like paracetamol and rest. Do not climb any higher and make sure you have had enough fluids to drink. Being dehydrated will make you feel more unwell. Your symptoms should settle over a few hours.

If you do not feel better within 24 hours you should descend to a lower altitude or seek medical advice urgently. If descent is easy, then do this without delay.

If you think you are developing HACE or HAPE, descending to a lower altitude is very important. If you are near medical facilities, then the doctors may put you in an altitude chamber (which mimics a descent) and may give you oxygen and specific drugs to help.

Can I prevent altitude sickness?

The main prevention is to ascend slowly and listen to your body – if you feel unwell, rest and recover. However, if this is not possible (for example, in a group situation) taking the tablet Diamox (acetazolamide) can help.

Taking Diamox twice a day, starting 24 hours before you ascend, reduces the symptoms of altitude sickness. Side effects can be a bit irritating, although not serious. Tingling hands, feet and face can occur, as well as fizzy drinks tasting flat. This medication is not currently available through our service, but your GP may be able to help you get a private prescription.