Altitude Sickness




Altitude sickness can occur when you travel to a high altitude too quickly.

Breathing becomes difficult because you aren't able to take in as much oxygen.

Altitude sickness, also called acute mountain sickness (AMS), can become a medical emergency if ignored.

Age, sex or physical fitness have no bearing on your likelihood of getting altitude sickness.

Just because you haven't had it before doesn't mean you won't develop it on another trip.

This page covers:

Symptoms of altitude sickness

Symptoms of altitude sickness usually develop between 6 and 24 hours after reaching altitudes more than 3,000m (9,842 feet) above sea level.

Symptoms are similar to those of a bad hangover.

They include:

  • headache
  • nausea and vomiting
  • dizziness
  • tiredness
  • loss of appetite
  • shortness of breath

The symptoms are usually worse at night.

It's not possible to get altitude sickness in the UK because the highest mountain, Ben Nevis in Scotland, is only 1,345m.


Consider travelling with these medicines for altitude sickness:

  • acetazolamide to prevent and treat high altitude sickness
  • ibuprofen and paracetamol for headaches
  • anti-sickness medication, like promethazine, for nausea

Preventing altitude sickness

The best way to prevent altitude sickness is to travel to altitudes above 3,000m slowly.

It usually takes a few days for the body to get used to a change in altitude.

You should also:

  • avoid flying directly to areas of high altitude, if possible
  • take 2-3 days to get used to high altitudes before going above 3,000m
  • avoid climbing more than 300-500m a day
  • have a rest day every 600-900m you go up, or every 3-4 days
  • make sure you're drinking enough water
  • avoid alcohol
  • avoid strenuous exercise for the first 24 hours
  • eat a light but high calorie diet
  • avoid smoking

Acetazolamide, available from a travel clinic and, in some areas, your GP, can help prevent symptoms. It's thought to help you adjust more quickly to high altitudes.

You should begin taking the medication 1-2 days before you start to go up in altitude and continue to take it while going up.

If using acetazolamide, you should still go up gradually and follow the general prevention advice.

If you get symptoms of altitude sickness while taking acetazolamide, you should rest or go down until you feel better before going up again.

Treating altitude sickness

If you think you have altitude sickness:

  • stop and rest where you are
  • don't go any higher for at least 24-48 hours
  • if you have a headache, take ibuprofen or paracetamol
  • if you feel sick, take an anti-sickness medication, like promethazine
  • make sure you're drinking enough water
  • avoid alcohol
  • don't smoke
  • avoid exercise

Acetazolamide can be used to reduce the severity of your symptoms, but it won't completely hide them.

Tell your travel companions how you feel, even if your symptoms are mild - there's a danger your judgement can become clouded.

You can continue going up with care once you feel fully recovered.

If you don't feel any better after 24 hours, you should go down by at least 500m (about 1,600 feet).

Don't attempt to climb again until your symptoms have completely disappeared.

After 2-3 days, your body should have adjusted to the altitude and your symptoms should disappear.

See a doctor if your symptoms don't improve or get worse.


If the symptoms of altitude sickness are ignored, they can lead to life-threatening conditions affecting the brain or lungs.

High altitude cerebral oedema (HACE)

High altitude cerebral oedema (HACE) is the swelling of the brain caused by a lack of oxygen.

Symptoms of HACE:

  • headache
  • weakness
  • nausea and vomiting
  • loss of co-ordination
  • feeling confused
  • hallucinations

A person with HACE often doesn't realise they're ill, and may insist they're all right and want to be left alone.

HACE can develop quickly over a few hours. It can be fatal if it's not treated immediately.

Treating HACE:

  • move down to a lower altitude immediately
  • take dexamethasone
  • give bottled oxygen, if available

Dexamethasone is a steroid medication that reduces swelling of the brain. 

If you can't go down immediately, dexamethasone can help relieve symptoms until it's safe to do so.

You should go to hospital as soon as possible for follow-up treatment.

High altitude pulmonary oedema (HAPE)

High altitude pulmonary oedema (HAPE) is a build-up of fluid in the lungs.

Symptoms of HAPE:

  • blue tinge to the skin (cyanosis)
  • breathing difficulties, even when resting
  • tightness in the chest
  • a persistent cough, bringing up pink or white frothy liquid (sputum)
  • tiredness and weakness

The symptoms of HAPE can start to appear a few days after arrival at high altitude. It can be fatal if it's not treated immediately.

Treating HAPE:

  • move down to a lower altitude immediately
  • take nifedipine
  • give bottled oxygen, if available

The medication nifedipine helps to reduce chest tightness and ease breathing.

You should go to hospital as soon as possible for follow-up treatment.

If you've had HAPE, you can register with the International HAPE Database to help develop new treatments for the condition.

'We were at high altitudes for four days and I was ill the entire time'

'We were at high altitudes for four days and I was ill the entire time'

Jessica Mathur, a GP from London, was surprised when she became ill with altitude sickness during a holiday in Peru.

"I was 19 and pretty fit when I went on a tour of Peru with two female friends. Like me, they were students who were looking for adventure.   

"We arrived late in the day at the city of Cusco in the Andes mountains, 3,500m above sea level.

"While sightseeing in the town the next morning, I began to feel unwell. Even when walking along a flat street I felt quite breathless and unable to keep up with my friends. I vomited, had a bit of a headache and generally had to do everything extremely slowly.

"I found it difficult to believe that I had altitude sickness. I just didn't expect it would happen to me. I recognised what it was because it's in every guide book.

"I became quite grumpy because I knew I was holding the others back. I tried to just do things that took the minimum effort, but that didn't help. I had nausea the whole time and felt 40 years older. 

"We travelled on by train to the lost Inca city of Machu Picchu, which is 2,430m above sea level. We were at these high altitudes for four or five days and I was ill the entire time.

"We weren't high up for the rest of the holiday, except during a hike in the Andes. My altitude sickness came back, which surprised me because we were in the foothills."

'Mild case'

"I only had a mild case and didn't have any serious consequences, but I couldn't really enjoy my time at high altitude much.

"We didn't do any real climbing in the mountains. I didn't think it was wise to go up any higher. The altitude sickness didn't affect my friends, and I found that annoying and a bit embarrassing because it just looked like I was very unfit. 

"I told my friends I thought I had altitude sickness. The warnings say you must make sure other people know about it because there's a danger that your judgement can become clouded. Because of this, some people often resist the advice to go to a lower altitude when it becomes necessary.

"As neither of my friends were affected, I thought it would be hard for them to believe I was feeling really unwell, but they were very understanding. 

"Nobody suggested I should go back down to a lower altitude. I wasn't so badly affected. I wanted to see the things we came to see and I felt lucky that the altitude sickness was mild.

"I haven't gone to a high altitude since then. I did have the opportunity to go up Mount Kilimanjaro in Tanzania, which is 5,895m above sea level, but I didn't want to go through altitude sickness again."

'Being careful to acclimatise properly did take extra time, but I was very glad I did'

'Being careful to acclimatise properly did take extra time, but I was very glad I did'

After years of mountain climbing, David Hillebrandt learnt how to deal with his altitude sickness.

"In 1980, my wife Sally and I drove to Kenya from Britain as part of a world drive. I suppose you could have described me as a tough and rugged young doctor and an experienced climber. Sally didn't climb at all.

"Before my ascent of Mount Kenya (5,199m), a technically challenging rock climb, we decided to walk the little-used but magnificent high-altitude trek around the mountain to acclimatise.

"It was quite a humbling experience for me as we progressed along the beautiful trail at between 3,000m and 4,000m. Sally was happy and healthy and enjoying the wonderful flora as we crossed amazing ridges and valleys, but she watched me being slowly overtaken by altitude sickness.

"I was soon suffering from a terrible, severe, throbbing headache worse than any hangover, and vomiting up everything I ate.

"We planned a celebration for my 27th birthday, but all I could do was be sick. Sally must have been tempted to laugh at me, a great mountaineer reduced to a liability.

"I must admit, I did slightly resent her apparent immunity to the horrors of altitude sickness. We're just genetically different."

'Fantastic dawn'

"I went down to a lower level for some relief from my aching head and enjoyed a good meal. That did the trick, and I was eventually able to climb the magnificent mountain in two days with no trouble.

"I couldn't have completed the rock climb if I'd been feeling ill. Being careful to acclimatise properly did take extra time, but I was very glad I'd done it.

"We got up to the summit in one day and dropped down about 100m to sleep tied to a ledge. Waking up to a fantastic dawn overlooking the African plains was something I'll never forget. It was certainly worth the effort, altitude sickness and all.

"Since then, I have become older and wiser, and I have learnt to go slower. I have climbed in the Himalayas and psychologically adapted to altitude sickness, but physically things are the same.

"It's still as bad as it was 30 years ago. The only difference is that now I know how to deal with it."