Altitude Sickness on Kilimanjaro: Prevention, Symptoms & What to Do
Everything you need to know to reach the summit safely
Everything you need to know to reach the summit safely
Altitude sickness is the number one reason climbers fail on Kilimanjaro. Not lack of fitness. Not bad weather. Not inadequate gear. It's your body struggling to function with half the oxygen it's used to.
About 75% of Kilimanjaro climbers experience some level of altitude sickness—from mild headaches to severe, life-threatening conditions. But here's the critical part: it's largely preventable if you understand what it is, recognize the warning signs, and know what to do.
This guide gives you the medical facts without the jargon, honest advice from guides who've summited hundreds of times, and practical strategies to maximize your chances of reaching Uhuru Peak safely. You'll learn which symptoms are normal, which are dangerous, when Diamox helps, and why your route choice matters more than your fitness level.
Let's get you to the summit—and back down—healthy.
Altitude sickness—medically known as Acute Mountain Sickness (AMS)—occurs when you ascend to high altitude faster than your body can adapt to reduced oxygen levels.
Here's the physics: at sea level, atmospheric pressure forces oxygen into your lungs efficiently. At Kilimanjaro's summit (5,895m / 19,341 ft), atmospheric pressure is roughly 50% of sea level. The percentage of oxygen in the air remains 21%, but the air is so thin that each breath delivers far fewer oxygen molecules.
Your body has amazing adaptive mechanisms—breathing faster, producing more red blood cells, increasing blood flow to vital organs. But these changes take time. If you gain altitude faster than your body can adjust, you develop altitude sickness.
AMS exists on a spectrum from mild to life-threatening:
Acute Mountain Sickness (AMS): The most common form. Symptoms include headache, nausea, fatigue, dizziness, loss of appetite, and difficulty sleeping. Uncomfortable but manageable with rest, hydration, and slow ascent. Most climbers experience mild AMS at some point.
High Altitude Cerebral Edema (HACE): A severe, life-threatening progression of AMS. Fluid accumulates in the brain, causing confusion, severe headache, loss of coordination (ataxia—inability to walk straight), altered consciousness, and potentially coma. HACE is a medical emergency requiring immediate descent.
High Altitude Pulmonary Edema (HAPE): Another life-threatening condition where fluid accumulates in the lungs. Symptoms include shortness of breath at rest, chest tightness, persistent cough (sometimes producing pink frothy sputum), extreme fatigue, and rapid heart rate. HAPE also requires immediate descent and oxygen.
The good news: HACE and HAPE are rare on Kilimanjaro when climbers and guides respond appropriately to early symptoms. The key is recognizing mild AMS and taking action before it escalates.
At what altitude does altitude sickness start? Most people begin experiencing symptoms above 2,500m (8,200 ft). On Kilimanjaro, you start around 1,800m and reach 5,895m within 5-9 days—a rapid ascent that challenges even healthy bodies.
Kilimanjaro presents a unique altitude challenge: you ascend from 1,800m to 5,895m in just 5-9 days. That's an altitude gain of over 4,000 meters in less than two weeks.
Compare this to other high-altitude treks:
Medical guidelines recommend not increasing sleeping elevation by more than 300-500m per day above 3,000m. Many Kilimanjaro routes violate this rule repeatedly, forcing your body to adapt on an aggressive timeline.
The second challenge: Kilimanjaro's accessibility. Unlike technical mountains requiring ropes and climbing experience, Kilimanjaro is a "walk-up" peak. This attracts people with little high-altitude experience who may not recognize symptoms or take them seriously until it's too late.
The third factor: commercial pressure. Budget operators use shorter routes (5-6 days) to reduce costs, sacrificing acclimatization. Climbers push through symptoms, afraid of "holding the group back" or wasting their investment.
This combination—rapid ascent, inexperienced climbers, and commercial pressure—makes altitude sickness the leading cause of summit failure and the primary safety risk on Kilimanjaro.
But it doesn't have to be this way. With proper route selection, pacing, and awareness, you can dramatically reduce your risk.
Recognizing altitude sickness symptoms early—and understanding their severity—is critical. Here's how to categorize what you're feeling:
Affects about 75% of climbers at some point, usually between 3,000-4,500m:
What to do: Rest at your current altitude. Hydrate aggressively—drink 3-4 liters of water per day. Take ibuprofen (400-600mg) for headaches. Eat even if you don't feel like it. Don't ascend further until symptoms improve, which typically takes 12-24 hours. Your guide will monitor you closely.
Mild AMS is uncomfortable but not dangerous if you respond appropriately. Most people adjust and continue without issue.
Symptoms escalate beyond uncomfortable into concerning:
What to do: Stop ascending immediately. Rest for at least 24 hours at your current altitude. If symptoms don't improve or continue worsening, descend 500-1,000m to a lower camp. Moderate AMS can progress to HACE or HAPE if ignored. This is not the time to "tough it out"—listen to your body and your guide.
These are medical emergencies. If you or a climbing partner shows any of these signs, immediate descent is mandatory:
HACE (High Altitude Cerebral Edema) symptoms:
HAPE (High Altitude Pulmonary Edema) symptoms:
What to do: Descend immediately—at minimum 500-1,000 meters, but ideally continue descending until symptoms improve. Administer supplemental oxygen if available. For HACE, administer dexamethasone (a steroid that reduces brain swelling). For HAPE, oxygen is critical.
HACE and HAPE can be fatal within 12-24 hours if untreated. Descent is the only cure—descending even 500m can be life-saving. No summit is worth your life. Professional guides know this and will make the call to descend if necessary.
Diamox (acetazolamide) is the most effective medication for preventing and treating altitude sickness. But it's a prescription drug with side effects, and opinions vary on whether everyone should take it. Here's the full picture:
Diamox is a carbonic anhydrase inhibitor. In simple terms, it makes your blood slightly more acidic. Your brain senses this acidity and responds by increasing your breathing rate—even at rest and during sleep.
More breathing = more oxygen intake = faster acclimatization. Diamox essentially forces your body to adapt more quickly to altitude by making you breathe the way you should be breathing at high elevation.
The benefit: Studies show Diamox reduces the incidence of altitude sickness by 50-75%. It's particularly effective at preventing the sleep disturbances common at altitude (periodic breathing—alternating between rapid breathing and breath-holding).
Prevention: 125-250mg twice daily (morning and evening). Some people start with 125mg to minimize side effects, others use 250mg for stronger effect.
When to start: Begin taking Diamox 1-2 days before ascending to altitude (many climbers start the day before flying to Tanzania). Continue through summit day.
When to stop: You can stop taking Diamox once you've descended below 3,000m, though some continue for 1-2 days post-summit.
Most people tolerate Diamox well, but side effects exist:
Serious concern: Sulfa allergy. If you're allergic to sulfa drugs (sulfonamides), you may be allergic to Diamox. Test it at home before your trip—never for the first time on the mountain.
Avoid Diamox if you:
Always consult your doctor before taking Diamox. Bring a prescription and test the medication at home to ensure you tolerate it.
Diamox is a valuable tool but not mandatory. Here's when we recommend it:
You may not need Diamox if:
Many climbers summit without Diamox. The best prevention is route choice, slow ascent, hydration, and listening to your body. Diamox is supplemental insurance, not a replacement for smart climbing.
Prevention is your best strategy. Here's what actually works, backed by medical research and decades of guiding experience:
Don't increase your sleeping altitude by more than 300-500m per day above 3,000m. This is the single most important prevention strategy.
Your body needs time to produce more red blood cells, increase breathing efficiency, and adjust to lower oxygen. Rushing this process causes altitude sickness.
The "climb high, sleep low" principle is key: hike to higher elevations during the day (exposing your body to thin air), then descend to sleep at a lower camp. This accelerates acclimatization without overwhelming your system.
Route choice determines whether you can follow this guideline. Longer routes (8-9 days) follow better acclimatization profiles. Shorter routes (5-6 days) force rapid ascent and higher AMS rates.
Target 3-4 liters of water per day. At altitude, you lose water rapidly through increased breathing (the air is extremely dry) and increased urination (your body's response to altitude).
Dehydration thickens your blood, making it harder to deliver oxygen to tissues. It also worsens altitude sickness symptoms.
How to know if you're hydrated: Your urine should be clear or pale yellow. Dark yellow or amber means you need to drink more. Drink before you're thirsty—thirst lags behind actual hydration needs at altitude.
Carry a water bottle and sip constantly during the hike. Drink tea or soup at camp. Yes, you'll pee frequently. That's the goal.
Altitude suppresses appetite. Food sounds unappealing, sometimes nauseating. But your body needs calories to function, generate heat, and adapt to altitude.
Carbohydrates are your friend. They're easier to digest at altitude and provide quick energy. Force down breakfast. Snack during the hike (trail mix, chocolate, energy bars). Eat dinner even when you'd rather skip it.
Undereating worsens fatigue, weakens your immune system, and hampers acclimatization. Our cooks prepare high-calorie meals for a reason—eat them.
Both suppress your respiratory system, reducing the oxygen your body desperately needs. Alcohol also dehydrates you and worsens sleep quality.
Save the celebratory beer for after you descend. On the mountain, stick to water and tea.
Sleeping pills are dangerous at altitude. They slow your breathing right when you need to breathe more. If you struggle to sleep (common at altitude), accept it. Rest your body even if sleep is restless. Lying down conserves energy.
This cannot be overstated: route choice is more important than fitness.
Routes with better acclimatization profiles have dramatically higher summit success rates and lower AMS incidence. Here's the breakdown:
Best acclimatization:
Moderate acclimatization:
Poor acclimatization:
The cost difference between a 6-day and 8-day climb is typically $400-800. That's $50-100 per extra day—a small price for 20-30% higher summit odds and a far more enjoyable experience.
See detailed acclimatization profiles on our route comparison page.
Covered in detail above. Diamox reduces AMS risk by 50-75%. Especially valuable if you're taking a shorter route or have a history of altitude sickness. Consult your doctor.
Route choice is the single biggest factor in whether you summit successfully. Here's how the main routes compare for acclimatization:
| Route | Duration | Acclimatization | Summit Rate |
|---|---|---|---|
| Northern Circuit | 9 days | Excellent | 95%+ |
| Lemosho | 8 days | Excellent | 90-95% |
| Machame | 7 days | Good | 75-80% |
| Rongai | 7 days | Good | 70-80% |
| Machame | 6 days | Fair | 60-70% |
| Marangu | 5-6 days | Poor | 50-65% |
Why Northern Circuit and Lemosho win: These routes incorporate multiple "climb high, sleep low" days. You hike to 4,600m during the day, then descend to sleep at 4,000m. Your body gets altitude exposure without the stress of sleeping high. By summit day, you're well-adapted.
Why Marangu struggles: You hit 4,700m on day 3. Your body has no time to adjust. Many climbers develop moderate AMS and turn back.
The cost-benefit calculation: An 8-day Lemosho costs about $2,200-2,600. A 5-day Marangu costs $1,600-1,800. The Lemosho costs $600 more but has 35% higher summit odds. If you travel internationally to climb Kilimanjaro, spending $600 to actually summit makes financial and experiential sense.
Learn more about each route on our detailed route comparison page.
Despite your best prevention efforts, altitude sickness might hit. Here's exactly what happens depending on severity:
Your guide will: Check your vital signs more frequently (pulse oximetry, heart rate, respiratory rate). Ask about symptoms. Slow the hiking pace or add a rest day. Encourage you to hydrate and eat. Most mild AMS resolves within 12-24 hours with rest at the current altitude.
You should: Hydrate aggressively (3-4L/day). Take ibuprofen for headaches (400-600mg every 6 hours). Eat even if you're not hungry. Rest as much as possible. Tell your guide immediately if symptoms worsen. Don't hide symptoms to avoid "slowing the group down"—your safety matters more than the schedule.
Your guide will: Stop further ascent. Add a rest day at your current altitude (12-24 hours). If symptoms don't improve, descend 500-1,000m to a lower camp. Administer oxygen if symptoms are concerning. Monitor closely for progression to HACE or HAPE.
You should: Follow your guide's instructions without debate. Rest completely. Hydrate continuously. Don't push through symptoms hoping they'll magically improve at higher altitude—they won't. Descent cures altitude sickness. Stubbornness kills.
Your guide will: Initiate immediate descent—minimum 500-1,000m, ideally continuing until symptoms improve. Administer emergency oxygen. Give dexamethasone (for HACE—a steroid that reduces brain swelling). Mobilize the team to assist—if you can't walk, porters will carry you on a stretcher (Gamow bag or wheeled stretcher). If descent isn't stabilizing you quickly enough, arrange helicopter evacuation.
You should: Follow instructions without argument. Don't minimize symptoms. Don't resist descent because you're "so close" to the summit. HACE and HAPE are life-threatening. People die from these conditions every year. Your life is more important than any mountain.
Real scenario: We've had climbers 100 meters from the summit turn back due to severe symptoms. We've descended through the night when someone showed signs of HACE. We've evacuated climbers from high camp. These decisions save lives. Professional guides prioritize safety over summit rates.
If descent and oxygen aren't stabilizing a climber, we call for helicopter evacuation. Helicopters can reach up to approximately 5,500m (weather permitting).
Helicopter evacuation costs $5,000-10,000 USD. Most helicopter companies require payment upfront or proof of insurance.
This is why travel insurance with high-altitude coverage is mandatory. Your policy must:
Reputable providers include:
Read the fine print. Some policies exclude "mountaineering" or cap altitude at 4,000m. Kilimanjaro is 5,895m. Ensure your policy covers the full altitude.
Don't cheap out on insurance. If you need evacuation and don't have coverage, you'll pay out of pocket—potentially bankrupting yourself.
Yes. Let's be honest: approximately 10 people die on Kilimanjaro each year, mostly from HACE or HAPE (though some deaths result from pre-existing medical conditions, hypothermia, or accidents).
That's 10 deaths out of roughly 35,000 annual climbers—a fatality rate of approximately 0.03%. For comparison, Everest's death rate is around 1-2%.
Why do people die from altitude sickness?
How to minimize your risk:
With proper acclimatization, professional guides, and honest self-assessment, your risk is extremely low. Most fatalities involve climbers ignoring symptoms or operators prioritizing speed over safety.
The bottom line: Kilimanjaro is serious but manageable. Respect the altitude, listen to your body, and trust your guides. Don't let fear paralyze you—let knowledge empower you.
The internet is full of advice about natural remedies for altitude sickness. Some have limited evidence, most are unproven. Here's what we tell climbers:
Ginger: May help with nausea. Bring ginger tea or ginger chews. Unlikely to prevent AMS but can make mild symptoms more tolerable.
Garlic: Some people swear by it, claiming it improves circulation. No strong scientific evidence, but it won't hurt (unless your tentmate objects to the smell).
Coca leaves (coca tea): Used traditionally in the Andes for altitude sickness. Not available in Tanzania. Also not proven to prevent AMS in clinical studies.
Ibuprofen: Effective for altitude headaches. Take 400-600mg every 6 hours as needed. Doesn't prevent AMS but treats one of the most common symptoms.
Ginkgo biloba: Mixed evidence. Some studies suggest it may reduce AMS risk; others show no benefit. If you want to try it, start 5 days before your climb (typical dose: 120mg twice daily). Consult your doctor, especially if you take blood thinners.
Aspirin: Some evidence suggests aspirin (325mg once or twice daily) may reduce AMS risk by improving blood flow. Low risk, low cost. Consult your doctor.
Our take: These remedies are supplemental at best. The proven strategies remain: slow ascent, hydration, proper route choice, and Diamox (if appropriate). If natural remedies give you peace of mind and don't interfere with proven strategies, go ahead. But don't rely on them as your primary prevention.
Focus on what works: choose an 8-9 day route, ascend slowly, drink 3-4L of water daily, eat consistently, and listen to your body.
About 75% of climbers experience mild symptoms like headache, nausea, or fatigue at some point. However, severity varies dramatically. Many people adjust within 24 hours. Choosing a longer route (8-9 days), ascending slowly, staying hydrated, and taking Diamox all reduce your risk significantly.
No. Physical fitness has no correlation with altitude sickness susceptibility. We've seen ultra-marathoners struggle at 4,000m and first-time hikers reach the summit easily. AMS is primarily genetic—how your body adapts to lower oxygen. Fitness helps with the physical demands but doesn't protect against altitude sickness.
Diamox reduces altitude sickness risk by 50-75%. It's especially recommended if you're prone to AMS, taking a shorter route (5-6 days), or want extra insurance. Many climbers summit without it by choosing 8-9 day routes and ascending slowly. Consult your doctor before deciding.
Severe warning signs include: confusion or altered mental state, inability to walk straight (ataxia), shortness of breath at rest, severe headache unresponsive to medication, persistent vomiting, or chest tightness. These indicate HACE or HAPE—life-threatening conditions requiring immediate descent and emergency oxygen.
The Northern Circuit (9 days) and Lemosho (8 days) have the best acclimatization profiles, with 90-95%+ summit rates. They follow the "climb high, sleep low" principle and give your body time to adapt. The Marangu 5-day route has the worst acclimatization (50-60% summit rate) due to rapid altitude gain.
Yes, approximately 10 deaths occur per year on Kilimanjaro, mostly from HACE or HAPE. However, with proper acclimatization, professional guides, and honest self-assessment, the risk is very low. The key is recognizing symptoms early and being willing to descend when necessary. No summit is worth your life.
Now you understand altitude sickness—what causes it, how to prevent it, how to recognize symptoms, and when to take action. You're better prepared than most climbers who show up without this knowledge.
Our team has guided hundreds of climbers safely to the summit. We know when to slow down, when to add rest days, and when to make the tough call to descend. We carry emergency oxygen, pulse oximeters, and emergency medications. We've handled mild AMS, moderate AMS, and—rarely but necessarily—HACE and HAPE situations.
We prioritize your health over summit rates. We won't push you beyond safe limits. We also won't let unfounded fear hold you back when you're doing well.
What we provide:
Ready to climb Kilimanjaro with a team that takes altitude sickness seriously? Let's talk about which route suits your experience level, timeline, and acclimatization needs. We'll make sure you're prepared, supported, and equipped with the knowledge to summit safely.
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