Skip to Content

Altitude Sickness (AMS)

Altitude Sickness Information - Mountain

Important: This information is for guidance only and should not be treated as medical advice, and should not replace guidance of a qualified medical professional. If in doubt at altitude, descend immediately and seek qualified medical attention.

  1. What is altitude sickness (AMS)?
  2. What causes altitude sickness?
  3. Common / normal symptoms
  4. Severe / dangerous symptoms
  5. Altitude sickness prevention


What is altitude sickness?

Altitude sickness has three forms. Mild altitude sickness is called acute mountain sickness (AMS) and is quite similar to a hangover - it causes headache, nausea, and fatigue. This is very common: some people are only slightly affected, others feel awful. However, if you have AMS, you should take this as a warning sign that you are at risk of the serious forms of altitude sickness: HAPE and HACE*. Both HAPE and HACE can be fatal within hours.


HAPE is excess fluid on the lungs, and causes breathlessness. It is never normal to feel breathless when you are resting - even on the summit of Everest. This should be taken as a sign that you have HAPE and may die soon. HAPE can also cause a fever (a high temperature) and coughing up frothy spit. HAPE and HACE often occur together.

If you think you may have had HAPE, please register with the International HAPE database.


HACE is fluid on the brain. It causes confusion, clumsiness, and stumbling. The first signs may be uncharacteristic behaviour such as laziness, excessive emotion or violence. Drowsiness and loss of consciousness occur shortly before death.

  • Immediate descent is absolutely essential
  • Dexamethasone and acetazolamide should both be given, if available
  • Pressure bags and oxygen gas can buy time

*HAPE stands for high altitude pulmonary oedema, and HACE for high altitude cerebral oedema. These medical terms simply mean 'fluid on the lungs/brain'.


What causes altitude sickness?

Two things are certain to make altitude sickness very likely - ascending faster than 500m per day, and exercising vigourously. Physically fit individuals are not protected - even Olympic athletes get altitude sickness. Altitude sickness happens because there is less oxygen in the air that you breathe at high altitudes.


Common / normal symptoms

The following symptoms will be experienced by most trekkers and when mild are usually nothing to worry about.

  • Shortness of breath, shallow breathing, panting
  • Mild headache
  • Dizzy spells, especially with sudden movement
  • Frequent urination (a good sign)


Additional hydration or a couple of paracetamol should cure or ease most of these symptoms. If you find they continue to worsen or if you experience any of the following severe symptoms, inform your guide immediately and consider descending to lower elevation.


Severe / dangerous symptoms

The following symptoms must not be ignored. While rare, they indicate potentially life threatening altitude sickness.

  • Severe headache, not cured by hydration or paracetamol
  • Hard, hacking chesty cough
  • Feeling of suffocation or squashed chest
  • Loss of co-ordination / drunk-like behaviour
  • Difficulty thinking or completing basic tasks
  • Coughing up blood


If you experience any of these symptoms you must inform your guide immediately and make plans to descend as far, and for as long as it takes for your symptoms to clear. Don't worry, on group treks there will be additional staff to stay with you so you don't hold the rest of the group back. Put your safety first.


Altitude sickness prevention.

Almost everyone will experience minor symptoms and that's OK.

Go up slowly, take it easy, and give your body time to get used to the altitude. The body has an amazing ability to acclimatise to altitude, but it needs time. For instance, it takes about a week to adapt to an altitude of 5000m.

Staying hydrated is crucial. During acclimatisation, we find drinking at least 1L of water for every 1000m of elevation (e.g. a minimum if 3L when we're between 3000m and 4000m until you're fully accimatised. You should be peeing very often (this is part of how we acclimatise) and it should be clear. You can reduce this after a few days at peak altitude, but should still ensure you drink plenty.

Remember: a happy mountaineer always pees clear!


Can I take drugs to prevent altitude sickness?

As with everything, many 'quack' treatments and untested herbal remedies are claimed to prevent mountain sickness. While we're all for doing things naturally, we can't vouch for these methods. These treatments have been claimed to make AMS worse or have other dangerous side effects that aren't fully understood. Only one drug is currently known to prevent AMS and to be safe for this purpose: acetazolamide (Diamox). It causes some minor side effects, such as tingling fingers and a funny taste in the mouth.


The most important thing to remember, is...

If you feel really bad during or just after an ascent - go down!




Share This


Read more Nepal Trekking Advice