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Altitude and Travel


Travelling to destinations at high altitude can be exciting, challenging and rewarding. Travellers going on high altitude excursions, treks or expeditions must research thoroughly, plan and prepare carefully (in some instances may include physical training) well in advance of travel, particularly if inexperienced in high altitude travel.

High Altitude Very High Altitude Extreme Altitude
Between 2400-3658m Between 3658-5500m Between 5500-8848m
  • Cochabamba, Bolivia
  • Bogota, Colombia
  • Quito, Ecuador
  • Cuzco, Peru
  • La Paz, Bolivia
  • Lhaza, Tibet
  • Everest Base Camp
  • Mt Everest summit
  • Mt Kilimanjaro 5895m

Good medical insurance that covers medical evacuation and repatriation is strongly recommended for those travelling to area of high altitude.

There are risks associated with high altitude including exposure to ultraviolet (UV) radiation, cold and the risk of developing altitude Sickness.

Climate Considerations

Sun Protection

The higher the altitude, the higher the exposure to UV radiation.

Protection against UV light should include:

  • wearing clothing that covers the skin and is impermeable to ultraviolet light
    • a facemask or balaclava may be required to protect against cold and sun at very high and extreme altitude
  • using a sunscreen that protects against UVA, UVB and UVC with a high sun protection factor (at least SPF15)
  • lips, ears and nose should be protected with a high protection sunblock
  • wearing sunglasses which filter out UV light.

Cold Protection

In areas at very high altitude, low temperatures combined with lower blood  oxygen levels increases the risk of frostbite. The risk is even greater in those who already have poor circulation. To help prevent injury from the cold:

  • wear correctly fitting clothes that are approved for cold climates; gloves, hats, socks, boots
    • a facemask or balaclava may be required to protect against cold and sun at very high and extreme altitude
  • keep hands and feet dry, change wet socks and gloves promptly
  • wear goggles at very high altitudes.


At altitude the air pressure is lower than at sea level and gets lower as you climb higher. This means that although the amount of oxygen in the air remains constant, the amount of absolute oxygen in the lungs and the blood is less.

Oxygen is necessary for energy and for the body to function normally. The body will adapt to lower oxygen levels and responds by breathing faster and deeper and making more red blood cells to carry oxygen around. This response, called acclimatisation, takes around 3-5 days to occur but will vary between individuals and environmental conditions.

Pre-existing Medical Conditions

If appropriate care is taken, most people can travel to high altitude destinations. However, travellers with certain medical conditions should seek expert medical advice pre-travel to ensure their condition is stable and will not be worsened by altitude. These conditions do not predispose to altitude sickness.

These include:

  • diabetes
  • epilepsy
  • heart conditions
  • lung conditions including chronic obstructive pulmonary disease and moderate/severe asthma
  • sickle cell disease.


Pregnancy is not thought to increase the risk of altitude sickness, but if it occurs it can cause reduced oxygen levels in the placenta, which may be dangerous to the fetus. Travel to altitudes up to 2500m is considered safe; the World Health Organization advises avoiding sleeping at altitudes > 3000m during pregnancy. Pregnant women travelling to altitude should consult their obstetrician and a specialist travel advisor pre-travel.

Altitude Sickness

Altitude sickness occurs if the body fails to, or has not had enough time to, acclimatise to altitude, the exact mechanism for this remains unclear.  The risk of altitude sickness increases with altitude; up to 25% will suffer at 2500m, whilst up to 75% will suffer > 4500m.

Altitude sickness at best is unpleasant; at worst it is a life-threatening condition that develops rapidly. There are three forms of altitude sickness:

  • Acute Mountain Sickness (AMS)
  • High Altitude Pulmonary Oedema (HAPE)
  • High Altitude Cerebral Oedema (HACE)

Acute Mountain Sickness

AMS is more likely to occur in those who do not take time to acclimatise properly or arrive directly at areas of high altitude e.g. Cusco in Peru (3300m). The higher and faster the ascent, the more likely that AMS will occur. Anyone can suffer from AMS regardless of age, gender, level of fitness or training.

Signs and Symptoms of AMS

Symptoms of AMS do not usually develop immediately upon arrival but occur between the first 4 - 36 hours at altitude.  There is a wide variation in the rate of onset and the height at which they occur. Early, mild symptoms are similar to that of a hangover:

  • headache
  • loss of appetite
  • nausea or vomiting
  • fatigue, flu like symptoms
  • dizziness
  • poor sleep and irregular breathing during sleep.

AMS can be diagnosed in adults using the a self assessment Lake Louise Symptom Score:

  • anyone who has recently ascended to over 2500m and has a score of 3 or more should be considered to have AMS

Treatment of AMS

  • be aware of the signs and symptoms of AMS and recognise them early. Let someone know that you are beginning to feel unwell
  • if early signs and symptoms of AMS are noticed then stop and rest at that level
    • do not go any higher
  • take analgesics to treat any headache e.g. ibuprofen or paracetamol
  • maintain a good fluid intake
  • once fully recovered ascent can begin again with care
  • if the symptoms of AMS do not improve over a day then descent of 500-1000m is necessary.

Acclimatisation and Prevention of AMS

There is no guaranteed way to prevent AMS but acclimatisation and slow ascent are strongly advised. Recommended rate of ascent at altitude according to expert guidelines are:

Recommendation Himalayan Rescue Association Wilderness Medical Society
Daily Assent 300m 500m
Rest Day Every 600m-900m Every 3-4 days
Maximum Daily Gain 800m No Recommendation

Gradual ascent is the most important preventive measure:

  • the major cause of altitude sickness is going too high too quickly

Those travelling in a group/tour are more at risk of AMS as the tour follows a set itinerary which may not suit all participants:

  • choose a trip with time for gradual acclimatisation built in
  • ideally avoid flying directly to areas of high altitude
  • take 2-3 days to acclimatise before going above 3000m
  • maintain a good intake (not excessive) of fluids
  • gentle exercise only for the first 2 hours
  • eat a light but high calorie diet
  • avoid alcohol.

Acetazolamide (Diamox)

Acetazolamide (Diamox) can prevent symptoms of AMS by increasing the rate at which the body acclimatizes. It may be considered in those susceptible to AMS or where a rapid ascent is unavoidable.  It can be prescribed by your GP or Travel Advisor if felt appropriate for you.

It should not be used as an alternative to a slow ascent.

The dose is 125mg Acetazolamide (Diamox) twice daily:

  • consider trial at sea level for two days before a visit to high altitude
    • commence 2- 3 days before ascent
    • discontinue 2-3 days after reaching highest sleeping altitude, or once descent has begun.
  • symptoms of AMS may still develop when on Acetazolamide (Diamox) and must not be ignored
  • if are allergic to sulphonamide antibiotics you may also be allergic to acetazolamide (Diamox) and it may therefore be inadvisable to take this drug.

Common side effects:

  • increased urine output (it is a diuretic); tingling in fingers/toes, facial flushing and altered taste, especially of carbonated drinks.

Common side effects:

  • dizziness, vomiting, drowsiness, confusion and rashes.

A range of other medicines and products (Coca tea in South America) have been suggested to be of benefit in preventing AMS. As yet there is not enough evidence to support the use of any of these substances.


If AMS is ignored and ascent continues then there is a real risk that either or both of the two serious forms of altitude sickness will occur: High Altitude Cerebral Oedema (HACE) and High Altitude Pulmonary Oedema (HAPE).

HACE is due to swelling of the brain occurs in approximately 1% of people who ascend to 3000m. Symptoms include:

  • severe headache
  • unsteadiness or inability to walk in a straight line heel to toe
  • vomiting
  • drowsiness
  • becoming confused or irrational.

HAPE is caused by fluid gathering in the lungs and is the most common cause of death from altitude sickness. Symptoms include:

  • breathlessness – this is progressive and will occur  at rest
  • marked fatigue
  • fast pulse
  • bluish discolouration of the skin (cyanosis).

Both conditions are medical emergencies and can be rapidly fatal; descent must be carried out immediately.

The person suffering from these conditions should be carried down to lower altitude; added exertion would worsen their condition. If descent is problematic, air evacuation by helicopter (if available) may be required.

Further Information

This website provides support for those carrying out medical expeditions. The Travel at High Altitude booklet is an excellent resource for those planning a trip at altitude and for carrying with them

British Mountaineering Council

British Mountaineering Council website is very comprehensive and informative with additional records on all aspects of health whilst mountaineering.

Lake Louise Symptom Score

Symptoms Severity Points

- No headache

- Mild headache

- Moderate headache

- Severe headache, incapacitating






- No gastrointestinal symptoms

- Poor appetite or nausea

- Moderate nausea or vomiting

- Severe nausea or vomiting, incapacitating





Fatigue and / or weakness

- Not tired or weak

- Mild fatigue/weakness

- Moderate fatigue/weakness

- Severe fatigue weakness, incapacitating





Dizziness / lightheadedness

- Not dizzy

- Mild dizziness

- Moderate dizziness

- Severe dizziness, incapacitating





Difficulty of sleeping

- Slept as well as usual

- Did not sleep as well as usual

- Woke up many times, poor nights sleep

- Unable to sleep.





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