Altitude sickness on a trek
Altitude sickness is the most common health problem on high treks, and the most preventable. Here is how it starts, the signs that mean you must go down, and how to give your body time to adjust.
This guide is general information, not medical advice. Talk to a doctor or travel clinic before a high trek, and on the mountain follow your guide and get medical help when symptoms are serious.
What altitude sickness is
Altitude sickness, or acute mountain sickness, happens when you go higher faster than your body can adjust to the thinner air. Anyone who sleeps above about 2,500 m without acclimatising is at risk, and sometimes lower.
Fitness does not protect you: training and fitness don't change the risk, and children are as likely to get it as adults. The best guide is how you reacted at a similar altitude before.
The symptoms
Headache is the main sign, usually with at least one of these:
- loss of appetite, nausea or vomiting
- dizziness
- unusual tiredness
- trouble sleeping
Symptoms usually start a few hours after reaching a new altitude, often during or after the first night. If you don't go higher, they usually ease within one to three days.
Danger signs that mean go down now
Altitude sickness can turn into two rare but life-threatening conditions: swelling of the brain (HACE) or fluid on the lungs (HAPE). Watch for:
- confusion, strange behaviour or unusual sleepiness
- losing balance or stumbling, as if drunk
- being breathless while resting
- a cough with frothy or bloody spit
- blue or grey lips or skin
Any of these is an emergency. Go down straight away if it is safe, with someone, and get medical help. Oxygen helps if your team carries it. Never leave a person with these signs alone.
If you feel unwell at altitude
- Tell your guide and your group. Hiding symptoms is how mild cases become serious.
- Don't go higher until the symptoms have gone. Rest at the same altitude.
- If you get worse, or you are no better after a day, go down. Descending 300 m to 1,000 m usually brings quick relief.
- Painkillers such as paracetamol or ibuprofen, or an anti-sickness medicine, may ease mild symptoms. They don't treat the cause, so don't use them to keep climbing.
How to acclimatise
- Go up slowly. Above 3,000 m, sleep no more than 500 m higher than the night before.
- Plan an extra night at the same altitude for every 1,000 m you climb, or every three to four days.
- Avoid going from below 1,200 m to a sleeping altitude above 2,750 m in a single day. A few nights at a moderate altitude before going higher help a lot.
- Take it easy for the first two days, drink enough water, and avoid alcohol and sleeping pills, especially early on.
- "Climb high, sleep low": walking up during the day and sleeping lower helps your body adjust.
Choosing a route and what to ask your operator
On a trek, the itinerary does most of the work. Longer itineraries add nights at middle altitudes and give your body time. On Kilimanjaro, for example, routes run from 5–9 days, and the shorter ones climb fast.
Before you book, ask the operator:
- how much higher you sleep each night, and where the rest days are
- whether guides are trained to recognise altitude sickness and check trekkers every day
- whether the team carries oxygen and a pulse oximeter
- what happens if someone must go down: who goes with them, and how evacuation works
Before you go
- See a doctor or travel clinic a few weeks before. Some trekkers are prescribed a preventive medicine, especially after past altitude sickness or for a fast ascent. Only a doctor can tell you whether it suits you.
- Get medical advice first if you have a heart or lung condition, diabetes, sleep apnoea, sickle cell disease or trait, or you are pregnant.
- If you plan to trek while fasting, for example during Ramadan, ask your doctor about it before you go: long hours without water add strain at altitude.
- Check that your travel insurance covers trekking up to the highest point of your route, including helicopter rescue.