Altitude sickness – a doctor’s story

Clinical Fellow at Bupa UK
24 January 2018

If you’re a keen traveller to exotic destinations, you may have found yourself somewhere at high altitude. While the views can be stunning and the experience exhilarating, there are risks – the main one being altitude sickness. Here I’ll explain what altitude sickness is, who’s likely to be affected and how to recognise it. You can also find out how to reduce your risk, and what to do if you become unwell.

Climbing Everest

I have experienced acute mountain sickness (AMS) three times – twice for understandable reasons (the third is less clear). For Kilimanjaro and the Salkantay trek to Machu Picchu, allowing more time for acclimatisation would have definitely helped. At Everest Base Camp I followed ‘the rules’ and still became unwell.

Interestingly, my twin brother and I both seem to get sick at different heights. For me it’s at a relatively humble 3,200m; for him at over 4,500m. The advantage of this is that we can both take care of each other at different parts of the trek!

Those who’ve had similar experiences will know the frustration of being surrounded by stunning scenery and fresh air, but unable to appreciate it because of nausea and a throbbing headache. 

On each occasion, I faced the same questions: I have limited time – can I cut out a day to fit more in? Should I pack medications just in case? I’m in pretty good shape; altitude sickness won’t affect me, will it? I even planned the Salkantay trek two weeks after Everest base camp in the hope that my acclimatisation efforts in Nepal would prevent further problems in Peru ... No such luck! 

What is altitude sickness?

At high altitude – generally above 2,500m and especially above 3,000m – breathing becomes difficult, as you aren’t able to take in as much oxygen as you can at sea level. Symptoms usually develop after 6 to 24 hours, and range from those similar to a bad hangover, to life-threatening problems such as going into a coma.

People can live comfortably at relatively high altitudes, but it takes time for the body to adjust and acclimatise to these conditions. 

Climbing Everest

Who is most likely to get altitude sickness?

Anyone! Age, sex or physical fitness do not play a part. In fact, the fitter you are, the faster you’re likely to make your ascent, so you may be at greater risk of becoming unwell.

What happens when you get altitude sickness?

In its mildest form AMS can feel like a hangover, with symptoms such as headache, nausea, vomiting, tiredness and dizziness.

More severe forms of altitude sickness can be life-threatening, affecting the brain and the lungs. These include high-altitude cerebral oedema (HACO) and high-altitude pulmonary oedema (HAPO). Both are medical emergencies and need urgent attention.

HACO is caused by swelling of the brain, with symptoms similar to AMS. It can also cause confusion, hallucinations and loss of co-ordination.

HAPO is the result of fluid build-up on the lungs and can lead to:

  • shortness of breath
  • chest tightness
  • cough with frothy phlegm 
  • a blue tinge to the skin (cyanosis)
  • swelling (for example a puffy facial appearance).

Symptoms will improve over several days if you stay at the same altitude or descend. If you continue climbing, symptoms may get worse and could become life-threatening. Symptoms of more severe forms of altitude sickness such as HAPO can take much longer to resolve, and may need to be treated in hospital.

Prevention of altitude sickness

The most effective way to prevent altitude sickness is to make sure you don’t increase your elevation too quickly. This is called ‘gradual ascent’. According to Wilderness Medical Society guidelines, above an altitude of 3,000m you shouldn’t increase your sleeping elevation by more than 500m per day. You should also take a rest day every three to four days.

Contact your doctor before your trip. They can assess your risk of altitude sickness based on your history of illness at altitude, and your anticipated rate of ascent. Based on this they may suggest medicine to help prevent altitude sickness, such as acetazolamide or dexamethasone.

They’ll probably give you acetazolamide, but dexamethasone may be better if you have an intolerance or allergy to acetazolamide. You should start treatment the day before ascent. Then stop it after two days at the highest sleeping altitude, or when starting your descent. Side-effects of acetazolamide include tingling in your fingers and toes, and needing to wee more frequently.

You’ll still need to ensure gradual ascent, as well as taking the medicines. Unfortunately neither of these will completely guarantee you won’t get AMS.

It’s worth knowing the different altitudes that you’ll be sleeping at on the trek, so your doctor can accurately calculate the risk.

It’s also recommended that you limit strenuous exercise for the first 24 hours after arriving at altitude, and drink plenty of fluid as you gain altitude.


For all types of altitude sickness, the main treatment is to descend to a lower altitude. You should descend until your symptoms improve, typically between 300 to 1,000m (though this varies from person to person).

If your symptoms are mild and limited to an altitude related headache or AMS, it may not be necessary to descend immediately. But climbing higher is certainly not recommended. Your headache may respond to medications such as paracetamol or ibuprofen. Acetazolamide may also relieve some symptoms by helping you to acclimatise.

If your symptoms don’t improve, get worse or you have any signs of HACO (poor coordination, confusion, drowsiness) you must begin descent and seek urgent medical attention. As well as descent, a doctor may consider other measures, such as supplementary oxygen or a portable hyperbaric chamber.

Climbing Everest

Would I do it again? 

Absolutely, in a heartbeat! Given my three previous encounters with AMS I will certainly pack acetazolamide for future trips. I would also recommend considering hiring your own guide, or going in a smaller group. This will give you the flexibility to remain at lower altitude for an extra day or two, if you need it.

I would also allow a few extra days in your travel itinerary. This will help if you need more time to acclimatise. But also if you have unexpected delays due to weather or transport issues.

Finally, I recommend erring on the side of caution and going with a guide wherever possible. At the summit of Kilimanjaro, it was our guide who noticed a member of a group showing subtle signs of confusion, and got him to a sensible height. I was far too busy taking photos!

On our trek to Everest Base Camp our guide helped me get medical attention when I started to experience symptoms of AMS. He also quickly got me and my brother to safety during a snow storm.

Unfortunately, there’s no way to guarantee that you won’t be affected by altitude sickness. However, proper preparation, being aware of the potential symptoms and when to seek urgent medical attention, will help to keep you safe.

Dr Tom Charlton
Clinical Fellow at Bupa UK

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