What is Altitude Sickness?

Thinking of heading off to visit the Ancient Inca ruins at Macchu Picchu high in the Andes in the Cusco region of Peru?

Altitude or ‘Mountain’ sickness is something you may want to think about before you travel.

Altitude sickness can occur at any height above 2,500m and usually occurs when a person climbs to a high altitude too quickly.

Macchu Pichu is set at around 2,430m above sea level. This means your likelihood of developing mountain sickness here is actually low. However, many travellers end up flying to or staying in Cusco before their trip to Macchu Pichu. Cusco is set at 3,310m above sea level. As this is considerably higher than 2,500m your risk of developing mild altitude sickness here is significant.

Furthermore, many ski resorts are set at 2,500m and those climbing mountains such as Kilimanjaro are at particular risk.

At high altitudes the air is ‘thinner’. This means that we inhale less oxygen for each breath that we take. Our body’s response is to:

  • Take more breaths- to get more oxygen
  • Increase production of red blood cells – as these carry oxygen


Altitude sickness is usually mild and will settle down after a couple of day’s acclimatisation and rest. Symptoms include:

  • Headache
  • Dizziness
  • Nausea
  • Exhaustion

However, in more severe cases altitude sickness can develop into more serious conditions related to fluid on the lungs and on the brain. These are quite rare but are more likely to occur in people who ascend rapidly to heights around 4,500m. Fluid on the lungs may be more likely in lung disease and you should check with your doctor before travel. Warning signs that warrant immediate medical attention and descent to the lowest possible altitude include:

  • Coughing up a pink or white frothy substance
  • Bubbling sound in the chest
  • Clumsiness or difficulty walking
  • Confusion or loss of consciousness

If you show mild symptoms of altitude sickness you should not ascend any higher for at least 24-48 hours to give your body time to recover. If symptoms improve after this acclimatisation phase, you can continue to climb.


There are many tricks and tips which can help.

  1. Avoid flying directly to a high altitude from a low altitude – this doesn’t give your body much chance to acclimatise.
  2. Give your body 2-3 days to acclimatise before going above 3000m.
  3. Avoid physical exertion- you may want to go on that hike across the Inca trail but your body is already working really hard to provide you with oxygen; give it time.
  4. Eat lots of complex carbs and avoid rich local foods at first – give your body some energy
  5. Drink plenty of water- one effect of mountain sickness can be dehydration
  6. Avoid alcohol as this can dehydrate your body further
  7. Do not climb more than 300m daily when above 3000m
  8. Have a rest day every 3 days
  9. Remember, exposure to UV radiation is greater at higher altitudes- use sunscreen and cover up
  10. Consider using a medication called Acetazolamide if gradual ascent is not possible
  11. Keep an eye out for signs and symptoms of acute mountain sickness and tell someone if you feel unwell.


If gradual ascent is not possible you can use a medication called Acetazolamide

Acetazolamide is a diuretic medication which also has the ability to acidify the blood. This increased acidity of the blood acts to stimulate more efficient breathing- particularly at night. Its overall effect is to reduce the duration of mountain sickness or eliminate it completely. It will make you urinate more so drinking plenty of water is crucial. It is not a magic bullet and you still have a risk of developing altitude sickness and even death in extreme cases, so you should always try to make a gradual ascent if at all possible.

The usual dose is half to one 250mg tablet twice a day for one to two days before and three days after the highest altitude is reached. You will need a prescription for this medication and it does NOT replace the measures outlined above.

A fairly common but minor side effect is tingling in your hands, feet or face. This will resolve when you stop taking the medicine but it can be psychologically distressing for some so seek advice if you are affected.


  • Ascend slowly
  • Give your body time to adjust at each altitude
  • Drink water
  • Eat well
  • Rest
  • Keep an eye out for warning signs

If your need any more information about any altitude sickness medicines feel free to contact us and our pharmacists will be able to advise you. Heading abroad and not sure what anti-malaria tablets you will need? Check out our Malaria Risk Map.

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