Altitude Sickness on Kilimanjaro
AMS kills summit bids. HACE and HAPE kill climbers. Here is what you need to know — the real version, not the watered-down tourist brochure version.
By Mount Kilimanjaro Climb — 9 min read
In 48 years of guiding on Kilimanjaro, our team has turned more climbers around than we can count. Never because they weren't fit. Always because the altitude got to them before the summit did.
The Three Conditions
AMS — Acute Mountain Sickness
What it is: The standard altitude response. Nearly everyone gets some version of this above 8,000 ft.
Symptoms: Headache, fatigue, loss of appetite, nausea, dizziness, poor sleep. Lake Louise Score of 3+ confirms AMS.
What to do: Stop ascending. Rest. Hydrate. Take ibuprofen for headache. If symptoms worsen over 24 hours — descend. AMS at altitude is not a badge of honor. It's a warning.
HACE — High Altitude Cerebral Edema
What it is: Severe AMS that has progressed to brain swelling. A medical emergency.
Symptoms: Severe headache unresponsive to ibuprofen, loss of coordination (ataxia), confusion, altered consciousness, inability to walk a straight line.
What to do: Descend immediately. Every 1,000 ft of descent can be lifesaving. Dexamethasone if available. No argument, no discussion — descent starts now.
HAPE — High Altitude Pulmonary Edema
What it is: Fluid in the lungs at altitude. More common than HACE. More fatal if not caught early.
Symptoms: Dry cough progressing to productive cough, breathlessness at rest (not just with exertion), rattling sound when breathing, blue lips or fingertips.
What to do: Immediate descent. Nifedipine if available. Your guide will organize a stretcher descent within minutes of diagnosis. HAPE kills within hours at altitude.
Prevention: What Actually Works
Real story: The ultra-marathoner who turned back
A client — we'll call him James — was a sub-3-hour marathoner. He trained for 6 months. He was the fittest person in his group. By Day 4 at Barranco (13,060 ft), he had a splitting headache and was vomiting every 20 minutes. His Lake Louise Score was 7/12.
Our guide sat with him for 2 hours. James wanted to continue. Our guide said: "You are the fittest person here. Your body is also the most confused — it has never been at this altitude. The mountain will be here next year. Your brain will not recover if we let this progress." James descended. He climbed again 8 months later and summited.
Fitness does not protect you from altitude. It gives you reserve. That is all.
The Pulse Oximeter: What It Tells Your Guide
Every Mount Kilimanjaro Climb guide carries a pulse oximeter. Blood oxygen saturation (SpO2) is measured every morning and evening above 12,000 ft. A healthy sea-level reading is 95 to 100 percent. At 15,000 ft, a well-acclimatized climber typically reads 85 to 90 percent. A reading below 80 percent — or a rapid drop from your previous reading — triggers an immediate management protocol.
Pulse oximetry is not alarmism. It is routine monitoring that allows guides to identify climbers who are struggling before symptoms become severe. Most operators on Kilimanjaro do not own a pulse oximeter. This means they are making decisions about climber safety without objective data. If your guide is not measuring your blood oxygen, ask why.
Real Story: When Descent Was the Only Option
A British climber on the Marangu Route — we'll call her Sarah — was 52 years old, hiked weekly in the Lake District, and had trained specifically for Kilimanjaro for 5 months. By Day 4 on the Marangu Route (which sleeps at successively higher altitudes every night), she had not eaten in 36 hours, was vomiting bile, and could not keep water down. Her SpO2 was 68 percent.
Our base camp coordinator received the radio call at 6am. Within 40 minutes, a stretcher team was dispatched from Horombo Hut. Sarah was assisted down to Marangu Gate. She was seen by a doctor in Moshi that afternoon. HACE was developing. Another few hours at altitude and she would have been in a life-threatening situation.
The Marangu Route is sometimes called the "Coca-Cola route" because of its comfortable hut accommodations. But it is also the route with the lowest success rate and the fastest altitude gain. Five days to the summit from 1,860m is too fast for most people. Sarah had no idea she was on the highest-risk itinerary when she booked. We now specifically advise against 5-day Marangu for first-time climbers, regardless of fitness.
What Our Guides Do
Every Mount Kilimanjaro Climb guide is trained in Wilderness First Responder protocols. Every trip carries:
- —Pulse oximeter — measured morning and evening above 12,000 ft
- —Diamox, Dexamethasone, Nifedipine in the medical kit
- —Gamow bag — portable hyperbaric chamber for severe HACE/HAPE
- —Stretcher team available for emergency descent within 30 minutes
- —Radio contact with base camp at all times
Frequently Asked Questions
Is altitude sickness random or can I predict if I will get it?
Altitude sickness is partly predictable. Prior history of altitude illness is the strongest indicator — if you struggled at altitude previously, you are more likely to struggle again. Age under 50 is paradoxically a risk factor because younger climbers tend to ascend faster and underestimate symptoms. Being male increases risk slightly. However, there is no test that reliably predicts individual response to altitude. This is why objective monitoring (pulse oximetry) and experienced guide judgment matter more than fitness assessments.
Can I take Diamox preventatively and skip the acclimatization days?
No. Diamox reduces the symptoms of altitude sickness but does not replace acclimatization. It works by stimulating the kidneys to excrete bicarbonate faster, which helps the blood carry oxygen more efficiently. But it cannot replicate the structural physiological changes that occur over days at altitude — increased red blood cell production, improved lung diffusion, enhanced capillary density in muscles. If you take Diamox and skip acclimatization days, you may feel better while still accumulating the same physiological risk.
What is the fastest way to descend if I develop HACE or HAPE?
On the Machame, Lemosho, and Northern Circuit routes, descent from Barafu Camp (4,700m) to lower camps takes 2 to 4 hours. In a genuine emergency, our guides will radio ahead and a vehicle will meet you at the trail head. On the Marangu Route, descent from Kibo Hut to Marangu Gate takes 5 to 7 hours on foot. For HACE or HAPE, every 1,000 ft of descent is medically significant. The Gamow bag — a portable hyperbaric chamber we carry — can buy time if immediate descent is not possible.
Does fitness reduce altitude sickness risk?
Fitness provides physiological reserve but does not prevent altitude sickness. The ultra-marathoner story in this article illustrates this clearly. Aerobic fitness improves oxygen utilization efficiency, which helps at altitude. But the risk of AMS is primarily a function of ascent rate and individual physiology, not aerobic capacity. A highly fit person who ascends too quickly will develop AMS just as readily as a less fit person who follows the same schedule.
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