Every year, climbers who have spent months training and thousands of dollars fail to reach the summit of Kilimanjaro. Most of them do not fail because of fitness. They fail because of altitude sickness. It is the single biggest reason people turn back — and it is largely preventable.
I have guided hundreds of climbs on this mountain. I have seen marathon runners collapse at 4,200 metres and retired teachers walk calmly into Uhuru Peak at 5,895. The difference was never strength. It was understanding how altitude works, respecting it, and making smart decisions along the way.
The Most Important Thing to Know
Altitude sickness is not about fitness. It is about how fast you go up. The slower you climb, the lower your risk. That is why every guide on Kilimanjaro says the same thing: pole pole.
What Is Altitude Sickness?
Altitude sickness — Acute Mountain Sickness, or AMS — happens when you climb faster than your body can adapt. At sea level, the air you breathe contains 21% oxygen. That percentage stays the same at 5,895 metres. But the atmospheric pressure drops, which means every breath pulls in fewer oxygen molecules. At the summit, you are getting roughly 49% of the oxygen your body is used to.
Your body can adjust, but it needs time. It needs to produce more red blood cells, increase your breathing rate, and change how it delivers oxygen to your organs. This process takes 24 to 48 hours per 1,000 metres of altitude gain. If you climb faster than that, your body falls behind — and AMS symptoms appear.
Most climbers start feeling it above 3,000 metres. By 4,000 metres, mild symptoms are common. The question is not whether you will feel something — it is how you respond to it.
Symptoms: What to Watch For
Altitude sickness comes in three stages. Knowing the difference between them is critical — because what you do at each stage determines whether you continue safely or end up in danger.
Mild AMS
- Headache — usually throbbing
- Nausea or loss of appetite
- Fatigue and weakness
- Dizziness, especially when standing
- Difficulty sleeping at altitude
- Mild shortness of breath
Moderate AMS
- Severe headache not relieved by ibuprofen
- Persistent nausea and vomiting
- Extreme fatigue — cannot walk normally
- Shortness of breath even at rest
- Decreased coordination — stumbling
Severe AMS (HACE / HAPE)
- Confusion or disorientation
- Inability to walk straight — ataxia
- Severe breathlessness at rest
- Coughing pink or frothy sputum
- Gray or pale skin colour
- Loss of consciousness
When to Descend Immediately
If you experience any symptoms of moderate or severe AMS, you must descend immediately. Do not wait to see if things improve. Do not push through. Descending 500 to 1,000 metres provides rapid relief — often within hours. Our guides carry pulse oximeters and check every climber's oxygen levels twice daily. If your numbers drop, we act fast.
What Increases Your Risk
Climbing Too Fast
The number one cause of AMS. If you rush the first two days, your body cannot keep up. Pole pole is not a suggestion — it is a survival strategy.
Altitude Gained Too Quickly
Most AMS symptoms appear above 3,500 metres. Routes that gain altitude too fast (like the 5-day Marangu) have the highest AMS rates.
Individual Susceptibility
Some people are genetically more prone to AMS. There is no way to predict this before you climb. Fitness does not protect you — biology does not care about your VO2 max.
Dehydration
Dry air at altitude causes rapid fluid loss through breathing and sweating. Dehydration worsens every AMS symptom. Drink constantly.
Overexertion
Pushing too hard increases your oxygen demand beyond what the thin air can supply. Walk at a pace where you can hold a conversation.
Not Eating Enough
Your body burns 50% more calories at altitude. Appetite drops at altitude — you have to force yourself to eat. Your muscles need fuel to function in thin air.
Proven Prevention Strategies
There is no magic pill for altitude sickness. But there are eight things that dramatically reduce your risk. Do all of them.
Choose a Route with Enough Days
Longer routes give your body more time to adapt. Seven or more days is strongly recommended for first-timers. The 5-day Marangu route rushes through acclimatization — that is why its success rate is only 60%.
Climb High, Sleep Low
Ascend to higher altitude during the day, then descend to sleep. This is the gold standard for acclimatization. Routes like Lemosho and Machame do this naturally with their terrain profiles.
Walk Slowly — Pole Pole
You should be able to hold a conversation while walking. If you are gasping, you are going too fast. Your guide sets the pace for a reason — follow it without questioning.
Stay Hydrated
Drink 3 to 4 litres per day. Monitor your urine — pale yellow means you are okay, dark yellow means you need more water. Your guide will remind you at every break.
Eat Enough Food
Your body burns 50% more calories at altitude than at sea level. Force yourself to eat even when your appetite is gone. Carbohydrates are especially important for energy at altitude.
Avoid Alcohol and Sleeping Pills
Both suppress your breathing rate, which is exactly what your body needs to increase at altitude. Skip the beer and the sleeping tablets for the entire climb.
Consider Diamox
Acetazolamide (Diamox) helps prevent AMS by stimulating breathing and speeding up acclimatization. Studies show it cuts AMS risk by about 50%. Consult your doctor before the trip and test it at home first.
Report Symptoms Immediately
Never hide symptoms from your guide. Never push through a headache hoping it will go away. The sooner you report, the sooner we can help. Mild AMS is manageable. Ignored AMS becomes dangerous.
Which Route Has the Lowest AMS Risk?
Route choice directly affects your risk. Longer routes with better acclimatization profiles have lower AMS rates and higher summit success:
| Route | Days | Success Rate | AMS Risk |
|---|---|---|---|
| Northern Circuit | 9 | 97% | Very Low |
| Lemosho | 8 | 95% | Low |
| Machame | 7 | 85% | Moderate |
| Marangu | 6 | 75% | Moderate-High |
| Marangu (5-day) | 5 | 60% | High |
The pattern is clear: more days equals lower AMS risk and higher summit success. The Northern Circuit at 9 days has the lowest AMS risk because it circles the mountain slowly, gaining altitude gradually. The 5-day Marangu has the highest risk because it forces rapid ascent.
I have never had a client on the 8-day Lemosho develop severe AMS. Not once. The extra days make that much difference. If you are worried about altitude sickness — and you should be, a little — choose a longer route. The extra cost buys you safety.
Altitude Sickness Myths That Put Climbers at Risk
"Fit people do not get AMS"
Completely false. Fitness has zero correlation with AMS susceptibility. Very fit athletes sometimes get AMS more often because they push harder and ascend faster. The biggest risk factor is speed, not strength.
"You can train for altitude at sea level"
False. Your body can only truly acclimatize by being at altitude. Altitude masks and hypoxic tents help marginally but cannot replicate the real thing. The only training that works is choosing a route with enough days.
"If you get AMS, your climb is over"
Not necessarily. Many climbers experience mild AMS — headache, nausea, poor sleep — rest for a day, and continue successfully. Mild AMS is your body adapting. It only ends your climb if you ignore it or push through.
"Diamox is a guaranteed fix"
It helps — studies show about 50% reduction in AMS incidence. But it is not a guarantee. Use it alongside proper acclimatization, slow pacing, and hydration. And test it at home first — some people get tingling fingers or altered taste.
Your AMS Prevention Checklist
- Choose a route with 7+ days for adequate acclimatization
- Walk slowly — pole pole — and rest when your guide says so
- Drink 3 to 4 litres of water every day
- Eat regularly, even when your appetite disappears above 4,000m
- Avoid alcohol and sleeping pills for the entire climb
- Consider Diamox after consulting your doctor
- Report any symptoms to your guide immediately — do not hide them
- Never ascend with AMS symptoms — rest or descend
- Trust your guide's experience and decisions completely
Frequently Asked Questions
Climb with Guides Who Know Altitude
Every Bush Lion Tours climb is led by guides trained in high-altitude health monitoring. We carry pulse oximeters, conduct twice-daily health checks, and make the call to descend when it matters. Your safety comes first — always.
