Altitude Sickness on Kilimanjaro

What is altitude sickness and why is Kilimanjaro such a test?

Altitude sickness is your body struggling with the lower air pressure, and therefore less available oxygen, at height. The air still contains about 21% oxygen, but each breath delivers less of it. At around 3,050 m the oxygen you breathe in is only 69% of sea-level pressure, according to the CDC.

Kilimanjaro is a hard test because it is high and it is quick. Uhuru Peak sits at 5,895 m, and most itineraries go from the gate at under 2,000 m to the summit in five to eight days. Compare that with Himalayan treks that take two weeks to reach similar heights.

There are three conditions to know:

• Acute mountain sickness (AMS): the common one. Unpleasant, usually manageable if you stop climbing.
• High altitude cerebral oedema (HACE): swelling of the brain. Rare but life-threatening.
• High altitude pulmonary oedema (HAPE): fluid in the lungs. Also rare, also life-threatening.

Altitude illness is usually described as starting above about 2,500 m. On most Kilimanjaro routes you pass that on the first or second day.

What are the symptoms of AMS?

The defining symptom of AMS is a headache at altitude, together with at least one of: poor appetite, nausea or vomiting, fatigue or weakness, and dizziness or light-headedness. These are the criteria used in the Lake Louise score and by the Wilderness Medical Society (WMS).

Symptoms usually appear several hours after arriving at a new, higher altitude. The NHS gives 6 to 10 hours; the CDC says 2 to 12 hours. In practice that often means the evening at camp or during the night, not on the trail. A bit of breathlessness when you walk uphill and a racing heart when you first lie down are normal responses to altitude and are not, by themselves, AMS.

Poor sleep is almost universal above 3,500 m. The 2018 revision of the Lake Louise score removed disturbed sleep as a scored symptom because researchers concluded it is a direct effect of low oxygen rather than a sign of AMS.

How do guides check you each day? (the Lake Louise score)

The Lake Louise score is a short questionnaire that turns "how do you feel?" into a number. The 2018 version, agreed by an international consensus group and published in High Altitude Medicine & Biology, rates four symptoms from 0 (none) to 3 (severe or incapacitating):

1. Headache
2. Gastrointestinal symptoms (appetite, nausea, vomiting)
3. Fatigue or weakness
4. Dizziness or light-headedness

A diagnosis of AMS requires a headache. Studies on Kilimanjaro have used a total of 3 or more as the threshold for AMS, and 5 or more for more significant AMS.

Many guiding teams pair the questionnaire with a pulse oximeter clipped to your finger. Treat the oxygen number with caution. A 2026 BMJ clinical review advises against using oximeters to diagnose altitude illness, because readings do not track reliably with symptoms. How you feel and how you walk matter more than the figure on the screen.

What are the signs of HACE and HAPE?

HACE and HAPE are the emergencies. Both can kill if the person is not taken down, and both can develop in someone who seemed only mildly unwell the evening before.

HACE (brain)

• Loss of coordination: stumbling, unable to walk heel-to-toe in a straight line
• Confusion, odd behaviour, slurred speech, extreme drowsiness
• Looks a lot like being drunk

The BMJ review notes that HACE can progress to coma and death within 12 to 24 hours without treatment and descent.

HAPE (lungs)

• Breathlessness far out of proportion to the effort, then breathlessness at rest
• A clear drop in your ability to walk compared with the day before
• Dry cough, then a wet cough; a gurgling feeling in the chest; sometimes pink, frothy sputum

HAPE mortality can reach 50% if untreated. HAPE does not always follow AMS, so a climber without a headache can still develop it.

The heel-to-toe walking test is simple enough that you and your tent-mate can do it on each other. If one of you cannot manage it, tell a guide straight away.

Why is descent the treatment that matters?

Going down is the most reliable treatment for every form of altitude illness. The WMS 2024 guidelines give descent a strong recommendation backed by high-quality evidence for AMS, HACE and HAPE.

How the response is graded:

• Mild AMS: stop ascending, rest at the same altitude, drink, eat if you can. Most cases settle within one to three days. Do not sleep higher while you still have symptoms.
• AMS that worsens or does not improve after a day: descend. The NHS suggests going around 300 to 1,000 m lower.
• Severe AMS, HACE or HAPE: descend immediately, day or night, with a guide. Supplemental oxygen or a portable hyperbaric bag buys time when descent has to wait.

On Kilimanjaro descent is usually possible: the trails are walkable and the gradient works in your favour. A 2022 study of 1,237 Kilimanjaro hikers in the Journal of Travel Medicine found that most kept climbing despite mild or severe symptoms, and that the only response associated with fewer severe symptoms was not climbing further. The study also found 1.1% of hikers were hospitalised with severe altitude illness.

What about medication?

Medicines can reduce the risk of altitude illness, but whether they are right for you is a decision for a doctor, not a trekking company. The WMS guidelines discuss preventive medication for people at moderate or high risk, and a Kilimanjaro itinerary that reaches 5,895 m is normally assessed as at least moderate risk.

Book an appointment with a travel-medicine doctor at least a month before you fly. Take your itinerary with the sleeping altitude for each night, and mention any history of altitude illness and any other medications you take. The CDC's Tanzania page gives the same advice: talk to your doctor about ways to prevent and treat altitude sickness.

Two points worth knowing before that appointment. First, no tablet replaces a sensible ascent profile or the rule of not climbing with symptoms. Second, the WMS and CDC advise against alcohol and sedating drugs that depress breathing at altitude, so be open with your doctor about anything you plan to take for sleep.

Who is most at risk, and can you reduce it?

The biggest risk factor is how fast you gain sleeping altitude, not how fit you are. The CDC states plainly that training and fitness do not reduce risk, and the 2026 BMJ review notes that younger, fitter trekkers can put themselves at greater risk by going too fast.

Other factors that raise risk:

• A previous episode of moderate or severe AMS, HACE or HAPE
• Sleeping above 2,800 m on the first night
• Gaining more than 500 m of sleeping altitude per day above 3,000 m without extra acclimatisation days

Things that lower it: choosing a longer route, walking slowly (the famous pole pole), staying well hydrated because dehydration mimics altitude illness, avoiding alcohol, and telling your guide about symptoms early. Our acclimatisation guide explains how route length changes the risk, and the route comparison puts the options side by side.

People with serious heart or lung disease, recent heart attack or stroke, sickle cell disease or a high-risk pregnancy may be advised not to go to high altitude at all. See your doctor well before booking.

What should I do before the climb?

• See a travel-medicine doctor with your day-by-day itinerary.
• Pick an itinerary of at least seven days if you can. The route finder can help.
• Check that your travel insurance covers trekking to 6,000 m and helicopter evacuation.
• Learn the HACE and HAPE signs above and agree with your group that anyone can call for a guide.
• Be honest at every health check. Guides can only act on what they are told.

If you want to talk through an itinerary with someone who walks these routes every season, you can ask Kili Aventura.

It depends heavily on the itinerary. A 2009 study of trekkers on 4 to 5 day Marangu ascents found 77% developed AMS, while a 2016 study of a 6-day Rongai ascent found 52.6%. A slower ascent lowers the risk but does not remove it.

Yes. HACE and HAPE are life-threatening, and deaths from altitude illness do occur on Kilimanjaro each year. Nearly all are preventable by recognising the warning signs and descending promptly.

Altitude illness can begin above about 2,500 m, and some people feel mild effects lower. On most routes the first night is spent at roughly 2,600 to 3,000 m, so symptoms can appear from the first or second night.

No. The CDC and a 2026 BMJ review both state that fitness is not protective. Fit climbers sometimes walk too fast, which can make things worse. Fitness helps you enjoy the trek, but it does not help your body adapt to less oxygen.

Tell your guide, drink water, eat something and rest. Do not climb higher to sleep until the headache has gone. If it gets worse, or comes with confusion, stumbling or breathlessness at rest, you need to descend.