Altitude Sickness
on Kilimanjaro
77% of climbers experience some AMS symptoms. Here's what that means — and why it's not the reason most people fail.
The difference between normal altitude discomfort and serious altitude sickness. When guides descend. How to prepare. What Diamox actually does. The science, straight.
77%
Experience some AMS
3%
Develop severe illness
95%
Summit success rate
Most climbers who experience AMS symptoms still summit. The rare climber who develops HACE or HAPE descends immediately. This page explains the difference — and why guides carry pulse oximeters, not just hope.
The Three Altitude Conditions
All occur because of low oxygen pressure, not lack of oxygen in the air itself. Understanding this distinction is key to not panicking.
AMS — Acute Mountain Sickness
The most common response to altitude. Mild to moderate. NOT dangerous if managed correctly.
Typical Symptoms
- • Headache (the most common)
- • Mild nausea
- • Fatigue
- • Insomnia at night
- • Mild shortness of breath
- • Dizziness occasionally
When It Occurs
- • Usually above 2,500m
- • Peaks around 3,000–4,000m
- • Symptoms improve by day 3–4 at same altitude
- • Worsened by rapid ascent
- • Worse at night than during day
What This Means
Your body is adjusting to lower oxygen pressure. This is normal and expected.
Do NOT interpret it as failure. Do NOT request descent. Unless your guide detects serious deterioration, AMS is not a reason to turn back.
HACE — High Altitude Cerebral Edema
Swelling of the brain tissue. RARE. Medical emergency. Immediate descent required.
Danger Signs
- • Severe headache not relieved by medication
- • Confusion or disorientation
- • Ataxia (loss of coordination, stumbling)
- • Altered consciousness
- • Hallucinations
- • Rapid deterioration of mental state
Frequency
- • 0.5–1% of climbers at 4,000m+
- • Higher in climbers who ascend too quickly
- • Can develop in 6–12 hours
- • Often preceded by AMS
- • Can occur even in fit climbers
Response Protocol
Immediate descent. No exceptions.
Our guides recognize these signs immediately. We do not wait. You descend 1,000m+ the same day. Descent is the only treatment that works.
HAPE — High Altitude Pulmonary Edema
Fluid in the lungs. RARE. Medical emergency. Immediate descent required.
Danger Signs
- • Severe shortness of breath at rest
- • Crackling sounds in chest
- • Pink or frothy sputum when coughing
- • Chest tightness
- • Blue lips or nail beds
- • Rapid, laboured breathing
Frequency
- • 0.5–1% of climbers at 4,000m+
- • Risk increases with rapid ascent
- • Can develop in 12–24 hours
- • Often occurs during sleep
- • Can occur even without prior AMS
Response Protocol
Immediate descent. Oxygen if available.
Our guides carry emergency oxygen. If HAPE is suspected, oxygen is administered and immediate descent begins. HAPE is survivable if descent happens quickly.
Why This Happens — The Science
Understanding the mechanism takes away some of the fear. You are not broken. Your body is responding to a real, measurable physiological change.
Lower Oxygen Pressure (Not Lower Oxygen in Air)
At sea level, atmospheric pressure is 101 kPa. At Uhuru Peak (5,895m), it is 34 kPa. The air contains the same percentage of oxygen (21%), but the density of that oxygen is much lower. Your lungs can extract oxygen less efficiently because there is less of it to extract. This is the fundamental cause of altitude sickness.
Hyperventilation Response
Your body detects low oxygen and breathes faster (hyperventilation) to try to extract more. This is automatic and helpful — it increases oxygen absorption. However, hyperventilation also lowers CO₂ in your blood, which makes your blood more alkaline. This alkalinity is one trigger for AMS symptoms (headache, nausea).
Fluid Shifts
Low oxygen pressure causes fluid to shift from blood vessels into surrounding tissue. Mild fluid shifts = mild AMS (headache). More significant fluid shifts in the brain = HACE. Fluid shifts in the lungs = HAPE. This is why descent is the only real treatment — you move to an altitude where normal oxygen pressure is restored and fluid returns to vessels.
Acclimatisation Process
Over 24–72 hours at the same altitude, your body adapts. Red blood cell production increases (to carry more oxygen). Your breathing pattern becomes more efficient. Fluid shifts stabilise. This is why our climbing schedules include acclimatisation days — they are not wasted time, they are the mechanism by which your body adapts to altitude.
Diamox (Acetazolamide) — What It Does & Doesn't Do
Diamox is not a cure. It is a tool that helps some climbers adapt more easily. Here is what the science shows.
✓ What Diamox Actually Does
- Changes kidney function to increase bicarbonate excretion (makes blood more acidic)
- Increases breathing rate — you breathe more efficiently and extract oxygen better
- Reduces sleep disturbances — sleep at altitude is often less broken on Diamox
- Modest reduction in AMS symptoms — about 50% of users report fewer headaches
- May reduce HACE/HAPE risk slightly — the research is less clear, but the effect appears real
✗ What Diamox Does NOT Do
- Does NOT increase oxygen in the air — the air above 4,000m is still the same (21% O₂, lower pressure)
- Does NOT allow unsafe ascent — taking Diamox does not mean you can climb faster
- Does NOT replace acclimatisation — rest days are still essential
- Does NOT prevent HACE/HAPE reliably — it lowers risk modestly but does not eliminate it
- Works for only ~50% of users — some people see benefit, some feel nothing, some dislike side effects
Typical Dosing & Side Effects
Standard dose: 125 mg twice daily (morning and evening), starting 2 days before your climb. Continue until summit or descent. Some climbers go higher (250 mg), some lower (125 mg once daily). Your doctor should advise.
Common side effects (usually mild and temporary):
- • Tingling in fingers, toes, lips (paresthesia — very common, harmless)
- • Increased urination (especially at night — annoying but normal)
- • Altered taste (fizzy drinks taste odd)
- • Mild headache or dizziness (usually resolves after 2–3 days)
- • Nausea (less common, usually mild if it occurs)
Serious side effects (very rare): Severe allergic reactions, Stevens-Johnson syndrome (extremely rare, occurs in ~1 per million users). Diamox is generally considered safe at recommended doses.
Diamox on Kilimanjaro — Should You Take It?
This is a personal decision made with your doctor. General guidance:
- Try: If you have a history of altitude sickness, or if you are taking rapid ascent options (Machame 6-day)
- Optional: If you are generally healthy and fit, on a 7-9 day route
- Discuss with your doctor: Always. They know your medical history. We do not.
Mount Kilimanjaro Climb Acclimatisation & Safety Protocol
Pulse Oximeter Checks — Every Camp, Every Day
We carry calibrated pulse oximeters. Your blood oxygen saturation (SpO₂) is measured at every camp above 3,000m. At rest, your SpO₂ should be 75–85%. Below 70% and we adjust the plan. Below 65% and we seriously discuss descent.
Walk-High, Sleep-Low Protocol
On acclimatisation days (e.g., Lemosho, Machame 7-day), we climb to a higher camp in the morning, rest and explore that afternoon, then descend to sleep at a lower altitude. This gets your body used to the elevation without forcing it to adapt while sleeping.
Daily Health Assessment
Every morning, our guides assess you: breathing, coordination, mental state, SpO₂, pulse, temperature. If something looks off, we slow down or adjust the day's plan. Most climbers never notice this, but it is always happening.
Oxygen on Every Climb
Emergency supplemental oxygen is carried on every expedition. It is rarely used, but when it is, it is the difference between continuing and descending. We do not cut corners on safety kit.
Clear Turn-Around Criteria
If your SpO₂ drops below 70%, or if you show signs of HACE or HAPE, we descend. The summit is not worth a medical emergency. Every guide understands this. No exceptions.
No Pressure to Summit
Your guide will not pressure you to summit if you are struggling. Reaching Stella Point (crater rim) is an extraordinary achievement. Many climbers turn back there and are proud of it. The mountain will be there next year.
Prepare for Altitude — Before You Arrive
Physical fitness matters. Training matters. Hydration in the weeks before matters. Here are resources to prepare.
16-Week Training Plan →
Build the fitness base that makes altitude easier to handle
Fitness Requirements →
What level of fitness do you need? How to assess yourself.
Summit Night Guide →
Mental and physical preparation for the hardest moment
Ready to Climb? Let's Plan It
Talk to one of our guides about your fitness level, medical history, and altitude concerns. We will build a route and acclimatisation schedule specifically for you.
Direct Question About Your Health?
WhatsApp Kassim — he'll advise based on your specific situation.
WhatsApp Kassim →Kilimanjaro Altitude Sickness — Ready to summit?
+255 786 110 786