Altitude sickness


Altitude sickness

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

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





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

coughing up pink, frothy liquid

clumsiness and difficulty walking

confusion leading to loss of consciousness

What to do if you have symptoms

If you have mild symptoms of altitude sickness, you should not 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 do not 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.

Preventing altitude sickness

Proper acclimatisation to altitudes of about 2,500m 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 are 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.

Who is affected?

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 have not developed it before does not mean that you may not develop it on a subsequent trip.



 Symptoms of mild altitude sickness

Symptoms of altitude sickness usually develop between six and 24 hours of being at high altitude. Common symptoms of mild altitude sickness (sometimes called acute mountain sickness) can be similar to a bad hangover and may include:


nausea and vomiting



loss of appetite

upset stomach

feeling unsteady

shortness of breath

increased heart rate

difficulty sleeping

generally feeling unwell

Symptoms of severe altitude sickness

The symptoms are usually worse at night. 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)



Severe symptoms could mean you are developing cerebral oedema or pulmonary oedema. These are potentially life-threateningcomplications 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.

Treating altitude sickness

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 into which you are zipped. The bag 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 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. Promethazine is an anti-emetic medicine often used by people with altitude sickness.

Acetazolamide (Diamox)

Studies have shown that acetazolamide, also available under the brand name Diamox, can help reduce the severity of altitude sickness symptoms, and can also help prevent the condition.

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

However, acetazolamide is not licensed in the UK for the treatment or prevention of altitude sickness and it is only available on prescription. Your GP may consider prescribing acetazolamide if they think it might be helpful, so you should talk to them about the possibility of using it before you travel.

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


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 medication 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 GP about the option of 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:




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 does not realise the seriousness of their condition, and may insist they are alright and only want to be left alone.

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.

Preventing altitude sickness

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.

When booking a trip yourself, try to include two or three days to acclimatise. If you are 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. 

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.


To prevent altitude sickness, acetazolamide can be 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 you may also be advised to take it for a day after you have reached your highest altitude.

The medication dexamethasone is not usually advised for the prevention of altitude sickness, but may be provided for the emergency treatment of high altitude cerebral oedema (HACE). See complications of altitude sickness for more information about HACE.

See treating altitude sickness for more information about acetazolamide and 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.

When ascending above 3000m, try to have a rest day every three days - when 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.

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 GP 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. 

What to pack


sun protection cream

lip balm

water purification system with iodine tablets

method of communication (mobile phones now work in some high altitude areas, including Kilimanjaro, but for other mountains you may need a satellite phone)

plastic whistle (six blasts and a pause is the internationally recognised distress signal)

headtorch and batteries