For the vast majority of climbers it is the altitude, and not the physical strain of several days of extended trekking, that poses the biggest challenge when attempting to summit Kilimanjaro.

The growth in the number of people climbing Kilimanjaro in the last decade, along with the development of rapid ascent routes to the summit, has sometimes led prospective climbers to underestimate just how much of a challenge climbing Kilimanjaro can really be. Kilimanjaro is classed as an extreme altitude (5,500m+) mountain climb, but it is sometimes assumed that Kilimanjaro is a comparatively easy high altitude climb. In fact, the failure rate among Kilimanjaro climbers is surprisingly high, with an estimated 40% of climbers failing to summit. In most failed summit attempts, the cause is altitude sickness.

Before you attempt to climb Kilimanjaro it is therefore most important that you have a good grasp of the risks associated with climbing at altitude. Learning how to identify and manage the symptoms of altitude sickness is among the most important steps in preparing for a Kilimanjaro climb. With this in mind, we’ve produced the following guide which we hope will help you better understand the risks of climbing at altitude, and how to reduce them.

You can also download an abbreviated version of our Kilimanjaro acclimatisation guide in PDF format from the Gane and Marshall website.

AMS – The risks

Acute Mountain Sickness (AMS) is the name given to the conditions that arise when the body fails to acclimatise properly to the reduced oxygen in the atmosphere that you experience at altitude. Typically, effects are not felt until you climb over 3000m above sea level. These conditions can take several forms: headaches, dizziness, nausea, insomnia and loss of appetite are the most common concerns. In this respect, AMS in its mildest forms is not dissimilar to a bad hangover. The main risks associated with AMS occur when it is not spotted early and these minor symptoms progress to the more serious conditions of HAPE (High Altitude Pulmonary Edema), caused by excess fluid in the lungs, and HACE (High Altitude Cerebral Edema), fluid on the brain. In the worst cases, these conditions can be fatal.

Keep in mind that all climbers will feel the effects of altitude to some degree. This is natural. Our bodies are not well adjusted to the high altitude, where reduced oxygen levels inhibit our normal physiological processes. Shortness of breath (dyspnoea) during exertion is universally felt by those climbing at very high or extreme altitudes; loss of appetite and insomnia are also common effects of altitude.

The fact that these symptoms are common can make it difficult to distinguish normal from abnormal effects of altitude, with the result that some climbers suffering from AMS push on in the belief that they are not at risk. As the symptoms of altitude sickness may not always be apparent to others, it is important that you are yourself able to recognise the symptoms of serious altitude sickness.

Generally, severe headaches (which do not go away with pain relief), extreme fatigue, prolonged dizziness, vomiting and dyspnoea while at rest are signs of serious AMS or HACE/HAPE and should prompt evacuation. But even the milder symptoms associated with AMS – tiredness, nausea, headaches – are a cause for concern if they are experienced for a prolonged period of time without abatement.

A final point to note about altitude sickness and its causes is that it is, to some degree at least, unpredictable. The effects of altitude do not appear to have much if any correlation to age and physical fitness. While some people seem to be more susceptible to its effects than others, everyone is at risk of suffering from AMS when climbing at altitude. Equally, there are steps that everyone can take to reduce this risk.

Preventing AMS

While your individual susceptibility to altitude sickness is hard to predict, some factors in its occurrence are predictable and can be managed. Factors such as the elevation at which you camp and your rate of ascent, for instance, have a bearing on how likely you are to suffer from altitude sickness. With this in mind, there are some basic rules you can follow to lessen the likelihood of suffering from serious AMS:

1. Ascend gradually – when climbing at altitude you need to give your body time to adjust to the reduced levels of oxygen in the air. Climb too quickly and you will greatly increase your risk of suffering from AMS. On Kilimanjaro, this means choosing a route that offers a gradual acclimatisation profile. See our notes below on choosing the right route.

2. Go slowly – Don’t over-exert yourself when climbing at altitude. Trek at a steady pace. Depending on your choice of route, most days on the mountain will see you trek for between 4 and 7 hours. There is nothing gained by rushing to the next camp more quickly.

3. Drink lots of fluid. The milder symptoms (headaches, dizziness, fatique) associated with AMS are often caused by dehydration. At high altitude (3,000m+) you lose water twice as quickly through respiration as at low altitude. It’s important to drink 3-4 litres of water a day. This won’t feel natural at first and it will mean drinking even when you don’t necessarily feel thirsty.

4. Preventative medication – Diamox is the only available drug for preventing altitude sickness. It is a prophylactic and helps prevent the onset of AMS; it does not cure it. Its side effects are few and generally very mild, though as a diuretic it does promote urination, meaning it’s especially important to drink lots of water while taking Diamox in order to replenish your fluids! Diamox is not essential but it is an effective prophylactic against mild AMS, though not severe altitude sickness.

5. Monitor your body – it is important to be aware of the most common symptoms of AMS, such as nausea, headaches, dizziness and shortness of breath, especially if you’ve never been to extreme altitude before. If you begin to suffer from any of these, however mild, let your guide know. If symptoms persist or get worse, do not continue to ascend. Vomiting, constant breathlessness (including at rest), and migraine are potential signs of severe altitude sickness and require evacuation.

AMS on Kilimanjaro – choosing the right route

The above advice could be applied to any high altitude climb. The advice that follows applies to Kilimanjaro specifically.

We’ve already stressed the importance of a gentle acclimatisation profile when climbing at altitude. This means choosing a route that takes you gradually to the summit, and, as much as possible, follows the climber’s adage of “climb high and sleep low”.

Unfortunately, many of Kilimanjaro’s routes encourage a very rapid ascent to the summit. Few 5,000m+ mountains are ordinarily climbed in 6 days, but on Kilimanjaro this is common. The ascent profiles of Kilimanjaro’s most commonly-trekked routes, such as the 5 or 6-day Marangu climb, compare very poorly to other popular treks such as Everest Base Camp in Nepal.

Whereas many treks have long walk-ins providing good acclimatisation before you even reach the mountain to be climbed, with Kilimanjaro you start right at the foot of the mountain from where a number of the routes take you on a more or less direct path to the summit.

One way around this issue is to add rest days. A route ordinarily climbed in 6 days, such as Rongai, can be extended with the addition of an extra day. Another way is to simply choose a naturally long route, such as Northern Circuit, Lemosho or Shira, which are typically climbed in 8-9 days without the need for rest days.

Also important is the elevation at which you camp. Lemosho and Shira routes are excellent in this respect in that they follow a more undulating trail giving you the chance to ascend to higher altitudes during the day before descending to lower altitudes to camp. This allows for a more gentle process of acclimatisation.

See our detailed route guide which provides an overview of all of the routes to Kilimanjaro’s summit, including our view on their respective acclimatisation profiles.

Finally, if time and money allow, you should consider a pre-acclimatisation climb or safari. Climbing Meru or Mt Kenya beforehand gives you a chance to adjust to the altitude before you’ve even set foot on Kilimanjaro. An altitude-acclimatising safari, involving light trekking in the Ngorongoro Highlands, is an alternative to the post-climb safari that many climbers anyway take.

For more information on altitude sickness and the best ways to prevent it, the charity Altitude provides very helpful and detailed information at The notes on altitude sickness by Dr Jim Duff of Treksafe are also valuable.