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Altitude sickness is the single biggest reason climbers do not reach the top of Kilimanjaro. It is also the most misunderstood. It does not depend on how fit you are, how young you are or how much hiking you have done. It depends on how quickly your body is asked to adapt to thinner air, and some people simply adapt more slowly than others. The good news is that the main risk factors are mostly within your control, and that a well-run climb has simple, reliable ways to spot trouble early.
In this guide
- What altitude sickness is, and why Kilimanjaro is different
- Symptoms, from mild to serious
- The three conditions: AMS, HACE and HAPE
- How to prevent altitude sickness on Kilimanjaro
- Diamox: what to discuss with your doctor
- How guides monitor you on the mountain
- What happens if you get sick
- Myths that put climbers at risk
- Choosing a route and itinerary that protect you
- Frequently asked questions
This guide is general travel information, not medical advice. Speak to a doctor or a travel clinic before your trip, especially if you have a heart, lung or blood condition, are pregnant, or take regular medicine.
What is altitude sickness, and why is Kilimanjaro different?
As you climb, the air pressure drops. The air still contains about the same proportion of oxygen, but each breath delivers less of it. At the summit of Kilimanjaro, 5,895 metres above sea level, there is roughly half the oxygen available at sea level. Your body copes by breathing faster, raising your heart rate and, over days, making more red blood cells. If you climb faster than that adaptation can keep up with, you develop altitude sickness.
Most high mountains take weeks of walking to reach. Kilimanjaro does not. You can start at the forest gate at around 2,000 metres and reach nearly 6,000 metres within a week. That speed, combined with the fact that anyone can book a climb without any mountaineering training, is what makes altitude illness so common here. Many people who would never think about trekking in the Himalayas attempt Kilimanjaro with no experience of altitude at all.
The symptoms of altitude sickness
Symptoms usually begin six to twelve hours after reaching a new height and are often worst the first night after a big gain. Medical bodies describe three levels.
Mild altitude sickness (acute mountain sickness, AMS)
- Headache, usually the first sign.
- Nausea, loss of appetite, or occasionally vomiting.
- Dizziness and unusual tiredness.
- Poor or broken sleep, vivid dreams or waking breathless.
These symptoms are common. Many climbers feel a mild headache at the high camps, and they are not on their own a reason to stop. They are a reason to slow down, drink, eat, rest and tell your guide honestly how you feel.
Warning signs that need action
- A headache that does not ease with simple painkillers and rest.
- Repeated vomiting.
- Needing to stop and rest after only a few steps on flat ground.
- A big drop in appetite and in energy that is out of proportion to the effort.
Emergency signs
- Confusion, strange behaviour or irritability that is out of character.
- Loss of balance or coordination, such as being unable to walk in a straight line.
- Breathlessness at rest, a persistent cough, or a rattling or bubbling chest.
- Blue lips or fingertips, or drowsiness that is hard to wake.
Emergency signs mean a descent at once. The right response is to go down, not to wait for morning and not to push on to the summit.
AMS, HACE and HAPE: the three conditions
Altitude illness is a spectrum. Almost all climbers who suffer have the mild form. A few develop one of two dangerous conditions.
- Acute mountain sickness (AMS) is the mild form described above. It is unpleasant but usually settles if you stop climbing and rest, and it is the stage at which good decisions make all the difference.
- High altitude cerebral edema (HACE) is swelling of the brain. It shows as confusion, loss of coordination and drowsiness, and can become fatal within hours if the person is not taken down.
- High altitude pulmonary edema (HAPE) is fluid in the lungs. It shows as breathlessness at rest, a cough, and weakness, and also needs immediate descent and medical care.
HACE and HAPE are rare on Kilimanjaro compared with the number of people who climb, but they do occur, and they are the reason guides take every symptom seriously. The most important rule in all altitude medicine is simple: if you have symptoms that are getting worse, do not go higher, and if they are severe, go lower.
How to prevent altitude sickness on Kilimanjaro
You cannot be sure of avoiding altitude sickness, but you can make it much less likely. These are the measures that work, in order of importance.
1. Choose a longer, more gradual route
The single most effective protection is time. An 8 day Lemosho climb or a 9 or 10 day Northern Circuit gives your body many more days to adapt than a 5 day Marangu or Umbwe climb. If you only change one thing about your plan, add days. Our guide to choosing a route explains the differences in detail.
2. Walk slowly: pole pole
The Swahili phrase pole pole means slowly, slowly, and your guides will say it dozens of times a day. A slow, steady pace keeps your heart rate down and your breathing controlled, which saves energy and reduces symptoms. The most common mistake we see is going too fast on the first day or two, when the trail feels easy. Walk at a pace that lets you hold a conversation.
3. Climb high, sleep low
Your body adapts best when you visit a higher altitude during the day and return to sleep lower. Routes such as Lemosho, Machame and the Northern Circuit build this in. On Lemosho the day from Moir or Shira to Lava Tower, at 4,630 metres, and then down to Barranco, at about 3,960 metres, is the classic example. Many climbers who feel poorly at Lava Tower feel much better by the time they sleep at the lower camp.
4. Drink plenty of fluid
Dry mountain air and fast breathing make you lose water. Aim to drink three to four litres a day, more of it as warm drinks, and watch for pale urine as a sign you are drinking enough. Dehydration can mimic and worsen altitude symptoms, so it is worth treating hydration as a task, not an afterthought.
5. Eat, even when you do not want to
Your appetite falls at height, but your body still needs fuel. Eat what you can at every meal, and carry snacks you actually like for the trail. A good camp cook will adjust meals to what climbers are able to eat.
6. Avoid alcohol and be careful with sleeping tablets
Alcohol dehydrates you and can hide symptoms, so most guides ask climbers to avoid it on the mountain. Sleeping tablets can slow your breathing at night when your body most needs to breathe deeply. Speak to your doctor before taking anything to help you sleep.
7. Be fit, but do not rely on fitness
Fitness helps you with the long days and steep sections and makes the whole experience more comfortable. It does not protect you from altitude sickness. Very fit people are sometimes among the worst affected, because they climb too fast. Our training guide covers how to prepare your body for the walking.
8. Tell your guide the truth
Your guide cannot see your headache. Do not hide symptoms because you are afraid of being sent down, and do not say you are fine to please the group. Honest reporting is the safest thing you can do on the mountain.
Diamox (acetazolamide): what to discuss with your doctor
Acetazolamide, sold as Diamox, is a prescription medicine that many doctors recommend to help prevent altitude sickness. It works by speeding up your body's adaptation to altitude. Guidance from wilderness medicine bodies suggests a low dose, started before or on the way up, but the right dose and whether it suits you is a decision for your own doctor.
- Common effects include tingling in the fingers and toes, needing to urinate more often, and a flat taste in fizzy drinks.
- It is related to sulfa drugs, so tell your doctor about any sulfa allergy.
- It is not a replacement for a gradual climb. It helps, but a poor itinerary still puts you at risk.
- It is not for everyone, including some people with kidney problems, certain allergies or pregnancy.
Ask your doctor or travel clinic well before your trip, so that you can try the medicine at home and see how you feel. Do not take medicine you have not tried before for the first time on the mountain. Many climbers also ask about a stronger steroid medicine used to treat severe altitude illness. That is an emergency treatment and is only used under medical direction, so it is not something to buy and carry on your own.
How guides monitor you on the mountain
A good operator does not leave altitude to chance. On a well-run Kilimanjaro climb you can expect the following.
- Daily health checks, usually in the morning and evening, in which the guide asks about headache, nausea, sleep, appetite and coordination.
- A pulse oximeter reading of your blood oxygen saturation and heart rate. Normal readings fall as you climb, so your guide looks at the trend and at how you look and feel, not at a single number.
- Written records, so that a decline in your numbers is spotted across days.
- The authority to stop a climber from continuing. A guide who would not turn you around is a guide to avoid.
- Emergency oxygen carried with the group, a first aid kit and a clear plan for evacuation.
Ask any company that you are thinking of booking with about its procedures. Look for specific answers about daily checks, who is trained in wilderness first aid, how many guides are in your group and what the evacuation plan is. For more on how to judge a company, see our guide to choosing a safari and trekking operator.
What happens if you get sick?
The treatment for altitude illness has one core principle: stop going up, and if you are getting worse, go down. In practice this looks like the following.
- Mild symptoms: rest, drink, eat, take a simple painkiller for the headache, and do not climb higher until you feel better. Your guide will monitor you closely.
- Symptoms that are not improving, or are getting worse: descend, even a few hundred metres. Often a drop in altitude is enough to feel much better.
- Emergency signs, such as confusion, loss of balance or breathlessness at rest: immediate descent, with oxygen if available. On Kilimanjaro, rescue teams can bring a sick climber down on a stretcher with a single wheel, and in serious cases a helicopter or vehicle takes them to hospital in Moshi or Arusha.
Turning back is not failure. Every year experienced climbers and guides turn around to protect their health, and almost all of those who descend quickly make a full recovery. The climbers who get into serious danger are nearly always those who ignored the signs.
Myths that put climbers at risk
- Myth: only unfit people get altitude sickness. Fact: fitness has little effect, and fast, fit climbers are often hit hardest.
- Myth: you can tell in advance who will get sick. Fact: past experience is the best guide, but even that is not certain, and you can be fine one time and ill the next.
- Myth: a headache means you must go home. Fact: a mild headache is common and manageable. A headache that does not improve, with other symptoms, needs action.
- Myth: a high pulse oximeter reading means you are safe. Fact: readings vary widely from person to person, and symptoms matter more than numbers.
- Myth: pills mean you can go faster. Fact: medicine may help, but it does not remove the need for a gradual schedule.
- Myth: you should push on to the summit because you have come so far. Fact: the summit is optional, your health is not.
Choosing a route and itinerary that protect you
The best way to reduce your risk is to choose an itinerary that builds in acclimatization. The longer routes that include a high day and a lower night, such as Lemosho over 8 days and the Northern Circuit over 9 or 10 days, are the strongest options. Our 10 day itineraries also use a daylight summit, so you climb in the light and not in the dark and cold hours after midnight, which many people find easier on the body and the mind.
If you are short of time, a 7 day Machame is the minimum we recommend for first-time climbers who are fit. If you want a hut, choose Marangu over 6 days with a rest day at Horombo. We advise against short 5 day versions for most people, because the schedule leaves too little room to adapt.
- 8-Day Mount Kilimanjaro Trekking Adventure via Lemosho Route
- 9 Day Mount Kilimanjaro Trekking Adventure via Northern Circuit Route
- 10 Day Mount Kilimanjaro Climbing Via Lemosho Route, Day Summit
Where the risk is highest on the mountain
Altitude sickness does not arrive evenly. On most routes there are a few moments where the risk climbs, and knowing them helps you plan your effort. On a Lemosho climb, for example, the first night at Big Tree Camp, at about 2,780 metres, is low enough that few people have trouble. The move up to Shira 1, at about 3,610 metres, and Shira 2, at about 3,850 metres, is where headaches often begin, and where an extra rest day pays off.
The day to Lava Tower, at 4,630 metres, is the highest point you reach before summit night and the point at which sensitive climbers often feel worst. It is also the heart of the acclimatization strategy, because you spend only a short time at that height and then descend to sleep at Barranco, at about 3,960 metres. After that comes the Barafu Camp stop, at 4,640 metres, which is the highest night most climbers spend, and the moment of the real test: the summit climb, up to 5,895 metres, where the air is at its thinnest.
On the Northern Circuit, the long sequence of nights at 4,000 metres and above, at camps such as Buffalo and Third Cave, gives your body repeated exposure, and that is why the route has such strong results. The lesson is the same whichever route you take: spend the days before the summit giving your body as many gentle steps up and down as you can.
Summit night and the final climb
Summit night is the hardest part for most climbers. On many itineraries you leave camp around midnight, in the cold and the dark, and climb for six to eight hours to Uhuru Peak, then descend for several more hours. The air is at its thinnest, the temperature can be well below freezing, and you are tired. Symptoms that were mild at camp can become sharp at the top.
Three habits make this night safer. Take it slowly, with short steps and a steady rhythm, so that you do not exhaust yourself early. Eat and drink at the stops, even if you do not want to, because cold and altitude suppress thirst. And agree in advance with your guide what the signals are for turning back, so that nobody has to argue at five thousand metres in the dark. A daylight summit, as used on our 10 day itineraries, removes the worst of the cold and the darkness, and many climbers find it much easier to judge how they feel.
Who needs extra care?
Some groups of climbers need to plan more carefully, and to speak to a doctor first.
- Older climbers. Age on its own does not stop you reaching the summit, and many people in their sixties climb successfully. A medical check, a slower schedule and a longer route matter more as you get older.
- Children. Altitude affects children too, and they may not be able to describe how they feel. Park rules set a minimum age for climbing, and we generally advise families to consider Mount Meru or a trek to the Shira Plateau first. Our Kilimanjaro guidance for families explains what is possible.
- Pregnant women. Climbing to this altitude is not advised during pregnancy, and anyone who is pregnant should speak to a doctor.
- People with heart, lung, blood or circulation conditions, or those who have had a stroke or high altitude illness before. These need medical advice and may need a more conservative plan.
- People taking regular medicines. Some medicines interact with altitude medicine or affect hydration, so review them with a doctor.
Sleeping and breathing at altitude
Poor sleep is almost universal at the high camps, and it is rarely a sign that something is wrong. Your breathing pattern changes at night in the thin air, with short pauses followed by deep breaths, and you may wake feeling short of breath. This usually settles once you sit up and take a few slow, deep breaths.
A few simple habits help. Keep warm, because cold makes everything worse, and use a good sleeping bag and a warm hat at night. Keep a water bottle inside your tent but, in freezing weather, protect it so that it does not turn to ice. Avoid heavy meals late in the evening, and try not to lie flat if your headache is bad. Many climbers find that raising their head and shoulders on a small pack eases the headache and helps them breathe.
What to do before you go
- See a doctor or travel clinic four to eight weeks before your trip, tell them about Kilimanjaro, and ask about altitude medicine, vaccinations and any health condition.
- Choose a longer itinerary and a company that is open about how it handles altitude.
- Train for the walking, with hills and long days in your hiking boots.
- Buy travel insurance that explicitly covers trekking to 6,000 metres, emergency evacuation and medical care.
- Pack for cold and wet weather, and bring a water bottle system you can use in freezing conditions.
- On the mountain, go slowly, drink, eat, and report every symptom.
Frequently asked questions
At what altitude does altitude sickness start?
Symptoms can appear from about 2,500 metres, and they become more common above 3,000 metres. On Kilimanjaro the higher camps are all above 3,500 metres, so some symptoms are common.
How many people get altitude sickness on Kilimanjaro?
Studies of trekkers report that a majority experience at least mild symptoms, and fewer experience severe illness. The exact numbers vary with route and pace, which is one reason longer itineraries help.
Can I train for altitude?
You can train your fitness, but you cannot fully train your body for altitude at sea level. Some climbers use altitude tents or spend time at height before the climb. Ask a doctor whether this suits you. A gradual route does the same job on the mountain itself.
Is Diamox necessary?
It is not necessary for everyone, and it is not a substitute for a good schedule. Many doctors recommend it for Kilimanjaro, so it is a conversation to have before you go.
Is it safe to climb Kilimanjaro with a health condition?
Many people with well-managed conditions climb, but you must talk to your doctor first, and tell your operator before you book. Conditions of the heart, lungs and blood need special care.
What if I feel ill at the high camp?
Tell your guide immediately. They will check you, and if you are not improving you will go down, often to a lower camp, where many climbers recover quickly.
Plan a safer Kilimanjaro climb
Keep planning your Tanzania trip
These guides cover the next questions most travellers ask.
Best Kilimanjaro route: every route compared
Kilimanjaro training plan and packing list
How much does it cost to climb Kilimanjaro?
How to choose a Tanzania safari company
Sources and further reading
Facts and figures in this guide come from the sources below. Fees, schedules and entry rules change, so confirm current details before you book.
- US Centers for Disease Control and Prevention (CDC) Travelers Health, Tanzania destination page, wwwnc.cdc.gov/travel.
- World Health Organization, International Travel and Health: yellow fever and malaria, who.int.
- Kilimanjaro National Park (Tanzania National Parks Authority), park information and fees, tanzaniaparks.go.tz and kilimanjaro.go.tz.
- Wilderness Medical Society, Clinical Practice Guidelines for the Prevention and Treatment of Acute Altitude Illness, wms.org.
- Lake Louise Consensus Group, the Lake Louise acute mountain sickness scoring system, widely used in travel medicine.
CDC Travelers Health: altitude illness
Last reviewed 7 October 2026. This guide is general information and does not replace advice from a doctor.