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Altitude sickness

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What is 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
  • Medication
  • Prevention
  • Treatment
  • Complications

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.


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.

Altitude sickness symptoms

Symptoms of altitude sickness usually develop between six and 24 hours of being at high altitude.

Symptoms of mild altitude sickness

Common symptoms of mild altitude sickness (sometimes called acute mountain sickness) can be similar to a bad hangover and may include:

  • headache
  • nausea and vomiting
  • dizziness
  • tiredness
  • loss of appetite
  • upset stomach
  • feeling unsteady
  • shortness of breath
  • increased heart rate
  • difficulty sleeping
  • generally feeling unwell

The symptoms are usually worse at night.

Symptoms of severe altitude sickness

Signs of severe altitude sickness can include:

  • worsening of the symptoms described above
  • a persistent, irritable cough
  • breathlessness (even when resting)
  • bubbling sound in the chest
  • coughing up pink or white frothy liquid
  • clumsiness and difficulty walking
  • irrational behaviour
  • double vision
  • convulsions (fits)
  • drowsiness

Severe symptoms could mean you are developing cerebral oedema or pulmonary oedema. These are potentially life-threatening complications of altitude sickness.

What to do if you have symptoms

If you have symptoms of mild altitude sickness, you should not go any higher for 24 to 48 hours. If your symptoms do not improve or get worse during this time, you should descend immediately.

Severe altitude sickness is a medical emergency. Someone with severe symptoms should immediately descend to a low altitude and seek medical help.

Read more about treating altitude sickness.

Altitude sickness treatment

If you have symptoms of mild altitude sickness, you should not go any higher for at least 24 to 48 hours.

Most cases will improve during this time, but it may help if you:

  • do not exercise
  • drink plenty of fluid (but not alcohol)
  • do not smoke
  • rest until you feel better

Make sure you tell the people you are travelling with how you feel, even if your symptoms are mild. This will help them be more aware of signs of severe sickness, such as irrational behaviour, if you develop them.

Descending to a lower altitude

If you have mild symptoms of altitude sickness that do not go away over 24 to 48 hours, the best thing to do is descend by at least 500m (about 1,600 feet).

Do not attempt to climb again until your symptoms have completely disappeared. After two to three days, your body will have acclimatised and your symptoms should disappear.

If you have severe symptoms or your symptoms are getting worse, descend immediately by as much as possible. This is because severe altitude sickness can be fatal if not treated quickly. Once you reach a low altitude, you should seek medical help immediately.

Oxygen treatment

Increasing your oxygen intake with bottled oxygen or portable hyperbaric chambers (also known as Gamow or Certec bags) can help temporarily improve some of the symptoms of altitude sickness.

A portable hyperbaric chamber is a bag you are zipped inside, which is then pumped full of air. After about two hours of treatment your symptoms should improve significantly. The effect of the treatment is equivalent to descending 2,000m (6,500 feet).

However, while oxygen treatment can relieve the symptoms of altitude sickness, it is not a replacement for descending to a lower altitude. You should always descend if you have severe or worsening symptoms, even if you've had oxygen treatment.



Painkillers, such as paracetamol or ibuprofen, can be used to treat mild headaches caused by altitude sickness.

Anti-sickness medication

If you are experiencing nausea or vomiting, a type of medication called an anti-emetic may be useful. Promethazin is an anti-emetic medicine often used by people with altitude sickness.


Acetazolamide can help reduce the severity of altitude sickness symptoms, and can also be used to help prevent the condition.

Altitude sickness can change the chemical balance of your blood. Acetazolamide helps correct this chemical imbalance.

As acetazolamide is a prescription-only medication, you should talk to your doctor about using it before you travel. There are a number of common but minor side effects associated with the drug, including numbness or tingling of the face, fingers or toes.


Dexamethasone can be very useful for treating severe complications of altitude sickness, such as high altitude cerebral oedema (HACE).

Dexamethasone is a strong steroid that reduces swelling of the brain. It's usually taken as a tablet several times a day.

The drug is particularly useful for "buying time" until it is safe to make a descent. For example, it can be used during the night to relieve symptoms when making a descent is not possible or may be dangerous. Symptoms usually start to improve within about six hours.

Dexamethasone can cause side effects such as stomach upset, difficulty sleeping (insomnia) and mood changes.

As with acetazolamide, you should talk to your doctor about taking dexamethasone before you travel.


Nifedipine is often used to treat high blood pressure, but it can also be useful in treating high altitude pulmonary oedema (see complications of altitude sickness for more information).

The drug decreases the narrowing of the artery that supplies blood to the lungs, helping to reduce chest tightness and ease breathing. It's usually taken as a tablet at six- to eight-hour intervals.

Nifedipine can cause a sudden drop in blood pressure, so it is important not to get up too quickly from a lying or sitting position if you take it.

Complications of altitude sickness

Although rare, altitude sickness can also lead to potentially life-threatening conditions affecting the brain or lungs.

High altitude cerebral oedema

High altitude cerebral oedema (HACE) occurs when a lack of oxygen causes fluid to leak through the capillary walls and into the brain, causing the brain tissue to swell. Capillaries are tiny blood vessels that surround major organs, such as the brain, heart and lungs.

Symptoms of HACE can include:

  • headache
  • weakness
  • disorientation
  • loss of co-ordination
  • memory loss
  • hallucinations and an inability to distinguish between reality and imagination
  • loss of consciousness, eventually leading to coma

HACE can occur if a person ascends to a high altitude rapidly or stays at a very high altitude for a week or longer.

If it is not treated immediately, it is likely that HACE will be fatal. To prevent this, immediate descent to a low altitude is necessary.

The steroid medication dexamethasone can be used to treat HACE. Oxygen also should be given if available. If possible, someone with the condition should be transferred to hospital quickly to receive follow-up treatment.

See treating altitude sickness for more information.

High altitude pulmonary oedema

High altitude pulmonary oedema (HAPE) occurs when fluid builds up in the lungs. The fluid prevents oxygen from being transferred from the lungs into the bloodstream. As the condition worsens, the amount of oxygen in the blood decreases, which can cause:

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

The symptoms of confusion and irrational behaviour are caused by a lack of oxygen to the brain. To prevent death, someone with HAPE should descend immediately to a low altitude.

Nifedipine is a medication that can be used to treat HAPE. However, as with HACE, someone with the symptoms of HAPE should be transferred to hospital as soon as possible for follow-up treatment.

See treating altitude sickness for more information.

The HAPE database

If you or someone you know has experienced HAPE, you can register with the International HAPE Database. The database has been set up to assist with research into this very serious health condition.

Jessica's story

Jessica, a trainee doctor 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.

"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 is 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."

Altitude sickness prevention

Proper acclimatisation to altitudes of 2,500m or above is the best way to prevent altitude sickness. Ascending slowly will give your body time to adapt to the change in altitude.

Before booking your trip, try to make sure you can take two or three days to acclimatise. Also avoid flying directly to a high altitude if possible.

Some itineraries are more likely to cause problems with acclimatisation than others. For example, a trekking holiday that involves crossing ridges or low peaks but sleeping in the valleys is less likely to give rise to problems with altitude sickness than a climb up an isolated peak such as Kilimanjaro.

Most walking, climbing or skiing holidays to the Alps involve sleeping in mountain huts at heights of around 3,000m above sea level or the use of valley bases, so severe altitude sickness is very unusual.

However, acclimatisation for the higher mountains in the Alps will make a successful ascent more likely and safer. Before setting out for peaks over about 3,500m, it is sensible to have spent a few days climbing lower peaks to acclimatise.

It is not only on trekking or climbing holidays that high altitudes are reached: for example, some parts of the Colorado Rockies can be reached by road despite being over 3,500m.

Climb gradually

Once you are above 3,000m (10,000 feet), do not increase the altitude at which you sleep by more than 300-500m a night. You can go up higher during the day, but each night go back down to a camp that is no more than 300-500m higher than the previous night's camp.

Some holiday companies offer to let you climb a mountain in a short time, such as climbing Mont Blanc over a couple of days. If you are not already acclimatised, climbing at this rate is likely to lead to symptoms of altitude sickness. It would be better to do it at the end of a two-week holiday after you have acclimatised by climbing a few lower peaks first.


There are some medicines that can help prevent altitude sickness as well as treat it.


To prevent altitude sickness, acetazolamide is taken twice a day. You should begin taking the medication two days before you start to ascend. Continue taking it while you are ascending and for at least two days after you have reached your highest altitude.

See treating altitude sickness for more information about acetazolamide.


Dexamethasone is usually taken twice a day to help prevent altitude sickness. It is normally taken for about two days, starting when you begin your ascent.

See treating altitude sickness for more information about dexamethasone.

Further advice

As well as acclimatising properly and taking prescription medication, follow the advice below:

  • If you start to develop mild symptoms of altitude sickness, stay at your current altitude until your symptoms improve.
  • If your symptoms get worse, immediately descend from your current altitude.
  • Make sure everyone you're travelling with has fully acclimatised before going any higher.
  • Try to have a full rest day every three days.
  • Keep well hydrated by drinking plenty of fluids.
  • Eat a high-calorie diet while at altitude.
  • Do not smoke, drink alcohol or use medication such as tranquillisers and sleeping pills while you are at altitude. They could make any symptoms of altitude sickness worse. Speak to your doctor if you are unsure.
  • Remember that the risk of sunburn and sunstroke is increased at altitude, so take full precautions to prevent them happening. In particular, make sure you have appropriate eye protection (specialist sunglasses, snow goggles or equivalent) and use them to prevent snowblindness, even if it is hazy.

Real stories

After years of mountain climbing, David 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 are just genetically different.

"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 had 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 will never forget. It was certainly worth the effort, altitude sickness and all.

"Since then, I have become older and wiser and I have learned to go slower. I have climbed in the Himalayas and psychologically adapted to altitude sickness, but physically things are the same. It is still as bad as it was 30 years ago. The only difference is that now I know how to deal with it."

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