Altitude sickness is the primary reason climbers fail on Kilimanjaro - not fitness, not weather. Here's what our guides wish every climber knew before they started walking.
The Most Important Thing to Understand
Altitude sickness has nothing to do with fitness. I have guided Olympic athletes who struggled at 4,500m and 60-year-old recreational walkers who bounded to the summit. The body's ability to acclimatize is largely genetic. You cannot train your way out of susceptibility - you can only manage it with the right pace, the right route length, and the right awareness of your own symptoms.
What Causes Altitude Sickness
At Uhuru Peak (5,895m), the atmospheric pressure means you're breathing air with approximately 49% of the oxygen available at sea level. Your body responds by breathing faster and deeper, producing more red blood cells, and adjusting blood chemistry. This process takes time - and if you ascend faster than your body can adapt, you get altitude sickness.
Three Types: AMS, HACE and HAPE
Acute Mountain Sickness (AMS) - Common and Manageable
AMS affects the majority of Kilimanjaro climbers to some degree. Symptoms typically appear 6 - 12 hours after a significant altitude gain:
- Headache (the defining symptom)
- Nausea or loss of appetite
- Fatigue disproportionate to effort
- Dizziness
- Poor sleep
Mild AMS is not dangerous. It is uncomfortable and demoralizing, but climbers can continue ascending if symptoms are mild and stable. The rule: if symptoms worsen with further ascent, do not continue.
High Altitude Cerebral Oedema (HACE) - Serious
HACE is severe AMS that has progressed to brain swelling. Symptoms: severe headache unresponsive to medication, loss of coordination (the "walk the line" test - ask the climber to walk heel-to-toe; inability to do so is a red flag), confusion, altered consciousness. HACE requires immediate descent. It is life-threatening if ignored.
High Altitude Pulmonary Oedema (HAPE) - Life-Threatening
HAPE is fluid accumulation in the lungs. It is the most lethal form of altitude illness and can develop rapidly. Symptoms: breathlessness at rest, dry cough that progresses to a productive (wet-sounding) cough, extreme fatigue, blue-tinged lips or fingernails. HAPE requires immediate emergency descent and emergency oxygen. It is the primary cause of altitude-related death on Kilimanjaro.
Prevention: The Golden Rule
"Climb high, sleep low." Acclimatize at a higher altitude during the day, but return to sleep at a lower altitude. This is built into well-designed routes like Lemosho and Rongai through the acclimatization day at Shira or Little Meru. It's why 8-day routes have meaningfully higher success rates than 6-day routes.
Practical Prevention Steps
- Choose an 8-day Lemosho or Rongai route over shorter options
- Hydrate aggressively - 3 - 4 litres per day on the mountain
- Walk slowly. "Pole pole" - slowly slowly - is not just a slogan
- Eat even when you don't want to - your body needs fuel to acclimatize
- Avoid alcohol on the mountain (vasodilator, worsens dehydration)
- Communicate symptoms to your guide honestly
Diamox (Acetazolamide) - Should You Take It?
Diamox is a carbonic anhydrase inhibitor that forces the kidneys to excrete bicarbonate, making the blood slightly more acidic, which stimulates faster breathing and speeds acclimatization. It works. Studies consistently show it reduces AMS incidence when taken correctly.
Typical dose: 125mg twice daily, starting 1 - 2 days before ascent above 3,000m. Side effects: tingling in fingers and toes (very common), increased urination, altered taste of carbonated drinks. Diamox is a sulfa drug - if you are allergic to sulfonamides, do not take it.
Consult your GP or a travel medicine clinic before Kilimanjaro. We strongly recommend it.
Our Guides' Role
Every Mashuba Tours guide carries a pulse oximeter and monitors blood oxygen saturation (SpO2) and heart rate at every rest stop. An SpO2 below 70% at Barafu Camp (4,673m) is a flag for closer monitoring. Our guides are trained in wilderness first aid and have standing orders to initiate descent if specific clinical thresholds are met - regardless of how close the climber is to the summit.
We have turned people around 200 metres from Uhuru Peak. It is always the right decision.
Expert guide at Mashuba Tours, sharing knowledge directly from the mountain and the field.