Altitude sickness

Altitude sickness


Altitude sickness is a common condition that can occur when you climb to a high altitude too quickly.

The decrease in atmospheric pressure makes breathing difficult because you aren’t able to take in as much oxygen. Most cases are mild, with symptoms that can include:

  • headache  
  • nausea
  • dizziness
  • exhaustion

In rare cases, altitude sickness can cause fluid to build up either on the lungs or the brain. These are very serious conditions and require immediate medical attention. Symptoms of severe altitude sickness can include:

  • a bubbling sound in the chest
  • worsening breathlessness 
  • coughing up pink, frothy liquid
  • clumsiness and difficulty walking
  • confusion leading to loss of consciousness

Read more about the symptoms of altitude sickness and the complications of altitude sickness.

What to do if you have symptoms

If you have mild symptoms of altitude sickness, you shouldn’t go any higher for at least 24 to 48 hours. You can continue to climb if your symptoms improve after this.

If your symptoms get worse or don’t improve after 24 to 48 hours, you should descend by at least 500m.

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.

Preventing altitude sickness

Proper acclimatisation to altitudes of about 2,500m (just over 8,200 feet) or more is the best way to prevent altitude sickness. It usually takes a few days for the body to get used to a change in altitude.

Ascending slowly will give your body time to adapt to the change in altitude. For example, once you’re above 3,000m (10,000 feet) try not to increase the altitude at which you sleep by more than 300-500m a night. Keeping hydrated is also important, but make sure you avoid alcohol.

Read more about preventing altitude sickness.

Who’s affected by altitude sickness?

Altitude sickness is fairly common among those who spend time at high altitudes, such as mountaineers and skiers.

In its mildest form, altitude sickness can occur at heights over about 2,500m (8,000 feet) above sea level, which is a common height for many ski resorts.

However, the more severe symptoms of altitude sickness tend to occur at altitudes of 3,600m (about 12,000 feet) and above.

It’s not possible to get altitude sickness in the UK because the highest mountain, Ben Nevis in Scotland, is only 1,344m (4,406 feet) high.

There are no specific factors, such as age, sex or physical fitness, that increase a person’s likelihood of getting altitude sickness. Certain people are affected, while others are less susceptible to it. Just because you haven’t had it before doesn’t mean you won’t develop it on another trip.

Symptoms of altitude sickness

Symptoms of altitude sickness usually develop between 6 and 24 hours after ascending to high altitude.

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.

Severe altitude sickness

Signs of severe altitude sickness can include:

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

Severe symptoms could mean you’re 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, don’t go any higher for 24 to 48 hours. If your symptoms don’t 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.

Treating altitude sickness

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

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

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

Make sure you tell the people you’re 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 don’t disappear over the course of 24 to 48 hours, the best thing to do is descend by at least 500m (about 1,600 feet).

Don’t 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 height as possible. This is because severe altitude sickness can be fatal if not treated quickly. Seek immediate medical help when you reach a low altitude.

Oxygen treatment

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

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

However, while oxygen treatment or the use of a hyperbaric chamber can relieve the symptoms of altitude sickness, it’s 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’re experiencing nausea or vomiting, a type of medication called an anti-emetic may be useful. Promethazine is an anti-emetic medicine often used by people with altitude sickness.

Acetazolamide (Diamox)

Research has shown that acetazolamide (Diamox) can reduce the severity of altitude sickness symptoms and can help prevent the condition.

Altitude sickness can change the chemical balance of your blood. It’s thought that acetazolamide helps correct this chemical imbalance.

In the UK, acetazolamide isn’t licensed for treating or preventing altitude sickness. However, it may sometimes be considered for use “off-label” to help prevent altitude sickness in people with a history of the condition. Read more about unlicensed medicines.

There are a number of common but minor side effects associated with acetazolamide, including numbness or tingling of the face, fingers or toes. Some people find these quite distressing, so doctors often suggest trying it at home for two days before travelling if you’re likely to use it at altitude.

You should let your doctor know if you have an allergy to any medicines before acetazolamide is prescribed. Your doctor will also check your medical history to see if acetazolamide is suitable for you.


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

This medication 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’s 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 that affect 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, resulting in swelling of the brain tissue. 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. A person with HACE often doesn’t realise the seriousness of their condition, and may insist they’re all right and want to be left alone.

If HACE isn’t treated immediately, it’s likely it will be fatal. Immediate descent to a lower altitude is necessary to prevent this.

The steroid medication dexamethasone can be used to treat HACE. If available, oxygen should also be given. Someone with HACE should be transferred to hospital quickly to receive follow-up treatment.

See treating altitude sickness for more information.


Dexamethasone can be very useful for treating severe complications of altitude sickness, such as high altitude cerebral oedema (HACE). It is a strong steroid that reduces swelling of the brain, and is usually taken as a tablet several times a day.

The medication is particularly useful for “buying time” until it’s safe to make a descent. For example, it can be used during the night to relieve symptoms when making a descent isn’t 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.

High altitude pulmonary oedema

High altitude pulmonary oedema (HAPE) occurs when fluid builds up in the lungs. The fluid prevents oxygen 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, but can also occur in high altitude cerebral oedema. To prevent death, someone with HAPE should descend immediately to a low altitude.

Nifedipine is a medication that can be used to treat HAPE. Dexamethasone may also be useful, although further studies are needed to assess its effectiveness.

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.

Preventing altitude sickness

Proper acclimatisation to altitudes of 2,500m (just over 8,200 feet) or above is the best way to prevent altitude sickness. Ascending slowly will give your body time to adapt to the change in altitude.

When booking a trip yourself, try to include two or three days to acclimatise. If you’re booking a package holiday, check the itineraries of different providers to find a package that allows a few days for acclimatisation. If possible, you should try to avoid flying directly to a high altitude.

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. 

It’s unusual to get severe altitude sickness during most walking, climbing or skiing holidays to the Alps. Overnight accommodation is usually in valleys or mountain huts at heights of around 3,000m (9,842 feet) above sea level. 

However, acclimatisation for the higher mountains in the Alps will make a successful ascent more likely and safer. Before setting out for peaks over 3,500m (11,482 feet), it’s sensible to have spent a few days climbing lower peaks to acclimatise.

It’s 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’re above 3,000m (10,000 feet), don’t 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’s no more than 300-500m higher than the previous night’s camp.

Some holiday companies offer trips to climb a mountain in a short space of time, such as climbing Mont Blanc over a couple of days. If you’re not already acclimatised, climbing at this rate is likely to lead to symptoms of altitude sickness. It would be better to attempt the climb at the end of a twoweek holiday after you’ve acclimatised by climbing a few lower peaks first.


Medicines would normally only be considered for preventing altitude sickness if rapid ascent cannot be avoided.


Research has shown that acetazolamide (Diamox, which is licensed to treat glaucoma) can help prevent symptoms of altitude sickness. It’s thought that acetazolamide works by correcting the chemical imbalance of the blood, caused by ascending quickly to high altitude.

In the UK, acetazolamide is not licensed for preventing (or treating) altitude sickness. However, it may sometimes be considered for ‘off-label’ use to prevent altitude sickness in people who may be at risk of developing it. Read more about unlicensed medicines.

To prevent altitude sickness, the recommended dose of acetazolamide is usually 125mg or 250mg twice a day. You should begin taking the medication one to two days before you start to ascend and continue to take it while ascending.

You may also be advised to take it for a day or two after you’ve reached your highest altitude. If you feel unwell while you’re ascending, acetazolamide will not prevent you feeling worse and the only treatment is to descend or to rest.  

There are a number of common but minor side effects associated with acetazolamide, including numbness or tingling of the face, fingers or toes. Some people find these quite distressing, so doctors often suggest trying it at home for two days before travelling if you’re likely to use it at altitude.

You should let your doctor know if you have any allergies to any medicines before acetazolamide is prescribed. Your doctor will also check your medical history to see if acetazolamide is suitable for you. 


Dexamethasone isn’t usually recommended for preventing altitude sickness, but may be provided for the emergency treatment of high altitude cerebral oedema (HACE).

Further advice

As well as acclimatising properly and taking prescription medication, you should also follow the advice outlined 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.
  • When ascending above 3,000m, try to have a rest day every three days – this is where you may climb higher, but return to sleep at the same altitude as the night before.
  • Keep well hydrated by drinking plenty of fluids.
  • Eat a high-calorie diet while at altitude.
  • Don’t smoke, drink alcohol or use medication such as tranquillisers and sleeping pills while you’re at altitude, as they could make any symptoms of altitude sickness worse. Speak to your GP if you’re unsure.
  • Remember, the risk of sunburn and sunstroke increases 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’s hazy. 

‘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. 

“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.”

‘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.

“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.”