Altitude Sickness on the Everest Base Camp Trek — Everything You Need to Know Before You Go

Altitude sickness, medically known as Acute Mountain Sickness (AMS), is your body’s reaction to lower oxygen levels at higher altitudes. The Everest Base Camp (EBC) trek begins at Lukla (2,860 m) and reaches EBC at about 5,364 m, where usable oxygen is roughly ~50% of sea level. Around 40% to 60% of trekkers develop mild AMS symptoms above 3,000 metres.

We at World Alpine Treks have guided hundreds of adventurers through this incredible journey, and understanding AMS is the first step to ensuring that your trek is safe, enjoyable, and memorable. In this guide, we’ll walk you through everything you need to know: how altitude sickness happens, how common it is, what symptoms to watch for, and how we help you prevent and manage it along the way.

What Is Altitude Sickness and Why Does It Happen?

Altitude sickness — medically known as Acute Mountain Sickness or AMS — is the body's reaction to reduced oxygen at high elevation. As you climb higher, atmospheric pressure drops, and with it, the amount of usable oxygen in every breath.

The Everest Base Camp trek begins at Lukla at 2,860 metres and reaches Base Camp at 5,364 metres. At that elevation, every breath delivers roughly 50% of the oxygen available at sea level. The body is essentially running on half its usual fuel supply.

To compensate, the body responds automatically — breathing faster, raising heart rate, and over time producing more red blood cells. These are intelligent, effective adaptations. The problem arises when ascent happens faster than the body can adapt. That is when AMS sets in.

Here is the part that surprises most of the trekkers: fitness has almost nothing to do with it. Cardiovascular strength, lung capacity, marathon times — none of it guarantees immunity from altitude sickness. We have seen highly fit athletes humbled above Namche Bazaar. We have also seen elderly first-time trekkers reach Base Camp without incident. The difference, almost every single time, comes down to one thing — acclimatization.

This is why most of the itineraries are built the way they are. Every rest day, every gradual elevation gain, every early stop — these are not schedule inefficiencies. They are carefully considered medical strategies, refined over hundreds of successful treks.

How Common Is Altitude Sickness on the EBC Trek?

In our experience, mild AMS is very common, and serious illness is rarely seen among trekkers who follow a well-structured program.

Research in trekking populations suggests that around 40% to 60% of trekkers develop mild AMS symptoms above 3,000 metres, particularly after rapid elevation gain.

Serious altitude illness — specifically HAPE (High Altitude Pulmonary Edema) and HACE (High Altitude Cerebral Edema) — is rare in properly structured itineraries, generally affecting fewer than 1–2% of trekkers.

These conditions are serious and demand immediate action, but they are almost always preceded by warning signs that trained guides are equipped to identify early.

The progression from mild symptoms to serious illness depends largely on the pace of ascent, early recognition, and appropriate response.

Oxygen Levels Along the Trek — Why This Matters

Understanding how oxygen availability changes with altitude helps explain why certain sections of the trek require greater care and attention. The drop becomes steeper the higher you go. Above Dingboche, the body is working hard even during rest. This is precisely why we monitor every trekker closely through the upper section of the route and why our guides do not treat the acclimatization days as optional.

Where on the Trek Does AMS Typically Begin?

Based on our collective experience across hundreds of EBC treks, symptoms rarely appear below Namche Bazaar. Most trekkers feel energised and motivated through the first few days. The altitude begins to make its presence known around 3,400–3,500 metres and becomes a genuine consideration above 4,000 metres.

 

This is why the itinerary includes dedicated acclimatization days at both Namche Bazaar and Dingboche. These are not rest days built in for comfort — they are medical necessities that trekkers treat with the seriousness they deserve.

Recognising the Symptoms of AMS on EBC

Early recognition is everything on a high-altitude trek. A symptom managed at the mild stage rarely becomes a crisis. A symptom ignored or pushed through can quickly escalate above 4,000 metres.

We communicate this clearly to every group before departure: if something feels off, speak up immediately. There are no toughness points on this mountain. The most sensible thing a trekker can do is report symptoms early.

Understanding the distinction between HAPE and HACE is important because they affect different organs — but both demand the same immediate response: descent without delay.

HAPE involves fluid accumulating in the lungs. A trekker will struggle to breathe even at complete rest. Our guides are trained to identify the characteristic sounds of respiratory distress at altitude and act immediately.

HACE involves swelling in the brain. A trekker may become confused, lose coordination, or behave unusually. This condition can deteriorate with alarming speed and constitutes a medical emergency requiring evacuation.

Both conditions are rare among trekkers on properly managed itineraries. Both are survivable when identified early. Both become far more dangerous when symptoms are minimised or ignored.

Prevention of Altitude Sickness on EBC Trek

Our prevention strategy has been developed and refined over years of guiding trekkers safely through the Khumbu. These are the methods our team trusts completely:

The 300–500 Metre Rule: Above 3,000 metres, our itineraries limit sleeping altitude gain to 300–500 metres per day. Every elevation profile in our EBC program is built around this principle. It is the non-negotiable foundation of safe high-altitude trekking, and our team does not compromise on it.

Climb High, Sleep Low: On acclimatization days at Namche and Dingboche, we lead hikes to higher elevations during the day before returning to sleep at a lower altitude. This method stimulates physiological adaptation without overwhelming the system. The science is well established — and our success rates on the trail confirm it every season.

Hydration as a Daily Discipline: We encourage every trekker to drink 3–4 litres of water daily throughout the trek. Dehydration accelerates AMS symptoms and makes every other challenge harder. We also advise limiting alcohol consumption above 3,000 metres, as it impairs sleep quality and reduces oxygen efficiency at precisely the altitude where both matter most.

Diamox — An Option, Not an Obligation: Acetazolamide, commonly known as Diamox, can support acclimatization by stimulating faster breathing. Our team neither prescribes nor discourages it — that conversation belongs with your doctor before the trek begins. What we will say clearly is this: Diamox is a support tool, not a replacement for proper pacing. 

Communication Between Trekker and Guide: Perhaps the most powerful prevention tool available is honest, open communication. Our guides build genuine relationships with every trekker in their group, specifically so that no one feels reluctant to raise a concern. The earlier a symptom is reported, the more options the team has to manage it effectively.

Can Beginners Safely Complete the Everest Base Camp Trek?

Absolutely. Most trekkers who follow a properly acclimatized itinerary successfully reach Everest Base Camp.

Beginners complete this trek successfully every single season with our team. The determining factors are not prior experience or athletic ability — they are a well-structured itinerary, experienced guides who monitor actively, and a trekker who approaches the mountain with patience and a willingness to listen.

Fitness is an asset. Respecting the acclimatization schedule and communicating openly with guides are what actually determine outcomes. The small percentage of trekkers who do not complete the trek share one consistent factor — they pushed against their guide's advice when it mattered most.

We have guided complete beginners to Base Camp safely for years, and we know exactly how to pace, support, and monitor first-time trekkers through every stage of the journey.

What To Do If AMS Develops on the Trek

If any member of a trekking group develops symptoms of altitude sickness, our protocol is clear, and our guides follow it without exception:

Stop ascending immediately: Not after the next tea stop. Not after reaching the planned camp. Immediately.

Inform the guide: Our guides need accurate information to make sound decisions. Every trekker in our groups understands before departure that reporting symptoms is not weakness — it is exactly what our team needs from them.

Rest at the current altitude for a minimum of 24 hours: For many cases of mild AMS, this is sufficient. The body catches up, symptoms ease, and the trek continues safely.

Descend 500–1,000 metres if symptoms persist or worsen: Descent is the single most effective treatment for altitude sickness. Even a relatively modest drop in elevation typically brings significant relief within hours.

For HAPE or HACE — evacuate without delay: Immediate helicopter evacuation is required. Our team maintains communication with rescue services and is trained to coordinate a rapid response in remote terrain. In these situations, evacuation procedures begin without hesitation.

Recovery timelines to expect: Mild AMS resolves in 24–48 hours with rest and hydration. After descent, even more significant symptoms often ease within hours. HAPE and HACE require hospitalisation and professional medical care — recovery may take days to weeks, depending on severity and how quickly the situation was addressed.

How Our Guides Monitor Every Trekker Daily

Safety monitoring at World Alpine Treks is not a background process. It is an active, structured part of how our team operates every single day on the trail.

Each morning and evening, our guides conduct individual check-ins with every trekker — covering headache, nausea, appetite, sleep quality, and energy levels. These are structured conversations, not casual enquiries. Our guides have encountered trekkers who insisted they felt fine while displaying three clear early indicators of AMS. Specific questions catch what general ones miss.

Our team carries pulse oximeters on every trek and monitors oxygen saturation and heart rate for all trekkers at key altitudes throughout the journey. A reading outside the expected range for that elevation triggers immediate assessment and, where necessary, a change of plan — regardless of how inconvenient that change may be for the schedule.

Our guides hold high-altitude first-aid certification and maintain active communication with our office team in Kathmandu. If an evacuation becomes necessary, our team can coordinate it rapidly. In terrain above 5,000 metres, the speed of that response can determine the outcome entirely.

The World Alpine Treks Safety Standard — What Every Trekker Receives

Every Everest Base Camp trek operated by World Alpine Treks includes the following as a baseline standard:

High-altitude first-aid certified guides accompany every group throughout the entire trek. Daily pulse oximeter monitoring for all trekkers at key altitude checkpoints, morning and evening. Itineraries are designed specifically around the 300–500 metre acclimatization rule, with no exceptions made for schedule convenience. Comprehensive pre-trek health briefings in Kathmandu covering AMS recognition, prevention, and emergency protocols. Active, maintained communication with helicopter evacuation services for the duration of the trek. Emergency insurance guidance is provided to all trekkers before departure.

These are not premium additions or optional upgrades. They are the standard our team holds itself to on every departure, because anything less is not acceptable on a mountain that demands this level of respect.

Frequently Asked Questions

How common is altitude sickness on the EBC trek? 

Studies suggest 40% to 60% of trekkers may develop mild symptoms above 3,000 metres. Most cases are manageable with rest and proper acclimatization. Severe conditions such as HAPE or HACE remain rare.

Does every trekker need to take Diamox? 

No. The majority of trekkers who complete EBC with our team do so without it. Gradual ascent, consistent hydration, and structured rest days form the real foundation of AMS prevention. Speak with your doctor before departure if you are considering Diamox — our guides do not administer or prescribe medication on the trail.

At what point on the trek does AMS usually appear? 

Our guides typically begin seeing mild symptoms around Namche Bazaar at 3,440 metres. The risk increases meaningfully above 4,000 metres, with Dingboche through to Gorakshep requiring the closest monitoring.

Can trekkers continue after mild AMS symptoms? 

Often yes — with rest, hydration, and close monitoring by the guide. Mild headaches that respond to water and rest are not always a reason to stop. Symptoms that persist, worsen, or are accompanied by dizziness and nausea require an honest assessment with the guide and potentially a change of plan.

Does physical fitness prevent altitude sickness? 

No — and this is one of the most persistent misconceptions our team works to correct. AMS is an acclimatization challenge, not a fitness challenge. The body's response to reduced oxygen at altitude is largely independent of cardiovascular conditioning. Patience and pacing protect trekkers far more reliably than athletic ability.

How quickly does altitude sickness improve? 

Mild symptoms typically ease within 24–48 hours of rest at the same altitude. After descending even a modest amount, relief often comes within a matter of hours. The body's response to lower altitude is generally rapid and noticeable.

A Final Thought

At World Alpine Treks, we have guided trekkers of every age, every background, and every fitness level through the Khumbu Valley to Everest Base Camp. We have seen the full range of what this mountain offers — its extraordinary beauty, its physical demands, and the profound sense of achievement that comes from standing at 5,364 metres beneath the world's highest peak.

Altitude sickness is not the enemy of this journey. Impatience is.

Every year, trekkers who rush the ascent, treat rest days as obstacles, or stay quiet about symptoms they should report, end up turning back before their goal — not because they lacked fitness, not because they were unlucky, but because they did not give the mountain the respect it requires.

And every year, trekkers who pace themselves, follow our team's guidance, stay hydrated, and speak up when something feels wrong — regardless of age, regardless of prior experience — stand at Everest Base Camp and feel something that words in any language struggle to capture.