This guide is general information, not medical advice. Talk to your doctor or a travel clinic before your climb, especially about medication and any health conditions.
Why altitude affects you
As you climb, the air pressure falls and each breath carries less oxygen. At Uhuru Peak (5,895 m) there is roughly half the oxygen available at sea level. Your body can adapt — by breathing faster, making more red blood cells and changing how it uses oxygen — but it needs time. When you climb faster than your body can adjust, you get altitude sickness. It can affect anyone, whatever their age or fitness.
The three forms of altitude illness
Acute mountain sickness (AMS)
Common and usually mild. A headache plus one or more of: nausea, loss of appetite, tiredness, dizziness and poor sleep. Mild AMS often settles with rest, fluids and not climbing higher until it improves.
High-altitude pulmonary oedema (HAPE)
Fluid in the lungs. Signs include breathlessness at rest, a persistent cough, a gurgling chest, blue lips and extreme tiredness. It is a medical emergency: the treatment is to descend immediately.
High-altitude cerebral oedema (HACE)
Swelling of the brain. Signs include severe headache that does not respond to painkillers, confusion, loss of balance or coordination, and drowsiness. It is a medical emergency: descend immediately.
How to prevent it
- Choose more days. The single biggest factor. A 7- or 8-day route gives your body far more time to adjust than a 5-day climb. See routes compared.
- Climb high, sleep low. Routes such as Machame and Lemosho climb to Lava Tower (4,630 m) and sleep lower at Barranco (about 3,950 m).
- Go "pole pole" — slowly. Walk at a pace where you can talk comfortably. Your guide sets it for a reason.
- Drink plenty. Aim for 3–4 litres of water a day.
- Eat, even without appetite. Your body needs the energy.
- Avoid alcohol and sleeping pills on the mountain.
- Be honest with your guide about how you feel, every day.
Medication
Some doctors prescribe acetazolamide (Diamox) to help the body acclimatise. It is not suitable for everyone and has side effects, so take it only on medical advice. It helps — it does not replace a sensible itinerary and a slow pace.
On the mountain
Your guides watch how every climber is coping and ask how you feel each day. Mild symptoms can often be managed by resting, drinking and slowing down. If symptoms get worse or signs of HAPE or HACE appear, the answer is to go down — quickly. Descending even a few hundred metres usually brings fast relief. Turning back is never a failure; it is the right decision. Read about rescue and insurance.
