Altitude Sickness on the Everest Base Camp Trek: How to Prevent It and What to Do

Everest Base Camp altitude sickness is a genuine risk but not a reason to panic. You travel from Lukla at around 2,860 metres to Everest Base Camp at 5,364 metres, sleep for several nights above 4,000 metres and may climb even higher to Kala Patthar. 

Obviously your body needs time to adjust at every stage.

Most altitude problems begin with symptoms such as a headache, nausea, dizziness or unusual tiredness. The important part is what happens next. Stop ascending, and mild symptoms will often improve. Ignore them and continue higher, and an uncomfortable day can develop into a medical emergency.

This guide explains where altitude becomes a concern on the route, how to recognise acute mountain sickness (AMS), how to reduce your risk and when turning back is the only sensible decision.

 

How common is Everest Base Camp altitude sickness?

Altitude sickness is common enough that every EBC trekker should understand it, but there is no single percentage that applies to every itinerary. Research groups use different definitions, routes and assessment methods. The speed of ascent also makes an enormous difference.

The CDC Yellow Book notes that even on standard Everest Base Camp acclimatisation schedules, the prevalence of altitude illness can approach 30% at higher elevations. It does not mean that 30% of trekkers develop a life-threatening condition. Many are mild AMS, but they still need to be taken seriously.

Your risk is affected mainly by how high you sleep, how quickly you get there and how your body responds. 

Important note: age, confidence, and cardiovascular fitness cannot guarantee protection. A very fit person can develop AMS while a slower, less athletic trekker remains well.

Why altitude sickness happens on the EBC route

The percentage of oxygen in the atmosphere remains roughly 21% at altitude. What changes is the air pressure. As atmospheric pressure falls, less oxygen is available to your body with each breath.

Your body responds by breathing faster and making other short-term adjustments. This acclimatisation process takes time. If your sleeping altitude rises faster than your body can adapt, symptoms can develop.

The EBC trek presents a particular challenge because most travellers fly from Kathmandu to Lukla. You land at around 2,860 metres and begin walking almost immediately. The first night in Phakding is lower, but you then make a substantial climb to Namche Bazaar. From there, you spend progressively more time at very high altitude.

Everest Base Camp altitude profile: where AMS becomes a concern

Base Camp is the headline altitude, but sleeping elevations matter more than the highest point you touch during the day. Most trekkers visit Base Camp and return to Gorak Shep rather than sleeping on the glacier.

The jump from Phakding to Namche raises your sleeping elevation by roughly 830 metres in one day. The trail has little practical accommodation between the two, so the following acclimatisation day in Namche is especially important. Later, the second acclimatisation stop in Dingboche gives your body more time before you sleep close to 5,000 metres at Lobuche.

Altitude measurements for Kala Patthar vary between maps and measurement points. For planning purposes, treat it as approximately 5,545 metres and concentrate on the ascent profile rather than arguing over a few metres.

Symptoms of altitude sickness on the EBC trek

AMS generally develops after an unacclimatised person ascends to altitude. Symptoms often appear several hours after arrival, which is why feeling fine at the teahouse door does not necessarily mean you will feel fine overnight.

Common symptoms include:

• Headache
• Loss of appetite
• Nausea or vomiting
• Dizziness or light-headedness
• Unusual fatigue or weakness
• Difficulty sleeping

Not every headache is AMS. Dehydration, cold, poor sleep, caffeine withdrawal and illness can produce similar symptoms. But a new headache or unexplained sickness after gaining altitude should not be dismissed. Tell your guide, consider the full pattern of symptoms and do not quietly continue upwards because you are worried about delaying the group.

Altitude sickness or another trail illness?

Stomach bugs, respiratory infections, dehydration and exhaustion also occur on the EBC trail. Their symptoms can overlap with altitude illness, and having another illness can make the physical effects of altitude harder to manage. Fever, diarrhoea, a sore throat or several people becoming ill after sharing food may point to another cause, but that does not make it safe to diagnose yourself and continue higher.

Tell your guide about every symptom and when it started. Wash or sanitise your hands before eating, treat drinking water properly and consider covering your mouth and nose on dusty sections of the trail. These precautions do not prevent AMS, but they reduce the chance of another illness confusing the picture or ending your trek.

AMS, HACE and HAPE are not the same thing

Altitude illness includes three main conditions. AMS is the common mild-to-moderate form. High-altitude cerebral oedema (HACE) affects the brain, while high-altitude pulmonary oedema (HAPE) affects the lungs. HACE and HAPE are medical emergencies.

Breathing hard while walking uphill is expected at 4,000 or 5,000 metres. Breathlessness while resting is different. Likewise, a tired trekker may walk slowly, but staggering, confusion, or an inability to walk heel-to-toe normally can indicate a serious neurological problem.

What to do if symptoms begin

1. Tell your guide or trekking partner immediately. Hiding symptoms to protect the itinerary puts you and the group at greater risk.
2. Stop ascending. Do not move to a higher sleeping altitude while symptoms remain.
3. Rest and reassess. Mild AMS can improve at the same elevation, often over one to three days.
4. Descend if symptoms worsen or fail to improve. Even a few hundred metres can make a meaningful difference.
5. Treat HACE or HAPE as an emergency. Descend, arrange medical help and use supplemental oxygen or a portable pressure chamber if trained support is available.
6. Never leave the affected person alone. Confusion can prevent someone from making safe decisions for themselves.

The mountain will still be there. Continuing upwards with worsening symptoms is not determination; it is removing your safety margin.

How to prevent altitude sickness on the Everest Base Camp trek

Choose a gradual itinerary

The most useful prevention strategy is giving your body enough time. Above 3,000 metres, recognised guidance generally recommends limiting increases in sleeping elevation to around 500 metres per day and including additional acclimatisation time as you climb higher. Terrain means an EBC itinerary will not match that number perfectly every day, so the overall pace and rest days matter.

Be cautious with itineraries designed mainly to advertise the shortest possible trek. Saving a day is poor value if it increases the chance of abandoning the trip.

Keep both acclimatisation days

Namche Bazaar and Dingboche should not be treated as optional sightseeing days. A good acclimatisation day normally includes a controlled walk to a higher elevation, followed by a return to the lower village to sleep—the familiar “climb high, sleep low” approach.

From Namche, trekkers commonly walk towards the Everest View Hotel or the villages of Khumjung and Khunde before returning to Namche. In Dingboche, the acclimatisation walk normally climbs one of the surrounding slopes before returning to the village. The objective is useful altitude exposure, not exhausting yourself by turning the day into a speed challenge.

Our 16-day Everest Base Camp trek includes acclimatisation time in both Namche and Dingboche before continuing towards Lobuche and Gorak Shep.

Walk slowly and control your effort

There is no prize for reaching the next teahouse first. A sustainable pace helps prevent exhaustion and gives you time to notice changes in how you feel. Fitness makes the walking more manageable, but it does not make you immune to altitude illness.

You can train for the demands of consecutive trekking days, hills, and carrying a daypack. You cannot train yourself to be immune to AMS at sea level. Pre-acclimatisation may help in some circumstances, but ordinary gym fitness does not predict who will become ill.

Stay normally hydrated

Drink enough to avoid dehydration, but do not force extreme quantities of water. Overhydration does not prevent AMS and can cause its own medical problems. Use thirst, urine colour, weather and your level of exertion as practical guides rather than treating a large fixed number as compulsory.

Avoid alcohol during the ascent

Alcohol can worsen sleep and dehydration and may suppress breathing. Avoid it while acclimatising, particularly during the higher part of the trek. Be cautious with sleeping tablets and other respiratory-depressing medicines unless a clinician familiar with altitude travel has advised you.

Build flexibility into the plan

An additional night can be useful when mild symptoms require rest. It cannot be guaranteed in every group itinerary, so ask the operator how extra nights, separation from the group and descent are handled before booking. Our complete guide to planning an Everest Base Camp trek covers the wider decisions around route, insurance, preparation and contingency time.

Should you take Diamox for Everest Base Camp?

Acetazolamide, commonly known by the brand name Diamox, helps the body acclimatise more quickly. It can be useful for some travellers, particularly when their ascent profile or history places them at greater risk. It is not a substitute for a gradual itinerary, and it does not make it safe to ignore worsening symptoms.

Common side effects can include tingling in the fingers or toes, increased urination, taste changes and nausea. Suitability depends on your health, medication and allergy history. Discuss it with a GP or travel-health clinician before leaving the UK rather than buying tablets on the trail and guessing how to use them.

Can a pulse oximeter diagnose altitude sickness?

A pulse oximeter can provide supporting information, but it cannot diagnose AMS by itself. Readings may be affected by cold fingers, movement, poor circulation, nail products and device quality. Healthy oxygen saturation also decreases naturally as altitude increases, and different people can function differently at the same reading.

There is no single percentage that automatically means every trekker must descend. Guides should consider the trend, the altitude and—most importantly—the person’s symptoms and behaviour. A reassuring number must never be used to dismiss confusion, loss of coordination or breathlessness at rest.

Common EBC altitude-sickness myths

Travel insurance and evacuation

Your travel insurance must cover trekking to the maximum altitude on your itinerary. Check for helicopter evacuation, medical treatment, repatriation, exclusions for pre-existing conditions and any requirement to contact the insurer before evacuation is arranged.

A helicopter is not an automatic free rescue service, and poor weather can prevent it from flying. Descent on foot may remain necessary. Carry your policy details and emergency contact information where both you and your guide can access them.

Review the health and emergency items in our Everest Base Camp packing list, but remember that equipment cannot compensate for an itinerary that ascends too quickly.

Can you trek to EBC after having altitude sickness before?

Previous AMS does not automatically rule out a future EBC trek, but it is important evidence. Your earlier response is most useful when the altitude and rate of ascent were similar. A slower itinerary, medical advice and a clear contingency plan may reduce your risk, but no plan can guarantee that symptoms will not return.

If you have previously experienced severe AMS, HACE or HAPE—or have a heart, lung, blood or sleep-related condition—speak with a clinician experienced in high-altitude medicine before booking.

Frequently asked questions

At what altitude can sickness begin on the EBC trek?

Altitude illness commonly becomes a concern above approximately 2,500 metres. Lukla is already around 2,860 metres, although the first night in Phakding is lower. Risk rises as sleeping elevations increase.

Is a headache normal at Everest Base Camp?

A headache may occur for several reasons, but it should never be automatically accepted as normal. After gaining altitude, treat a new headache—especially with nausea, dizziness, poor appetite or unusual fatigue—as possible AMS and tell your guide.

Can you continue trekking with mild AMS?

You should not ascend to a higher sleeping altitude while symptoms remain. Rest at the same elevation and continue only after symptoms have resolved. Descend if they become worse or fail to improve.

Does Diamox guarantee that you will not get altitude sickness?

No. It can help acclimatisation but cannot guarantee prevention. You still need a sensibly paced itinerary and must respond appropriately to symptoms.

Do EBC trekkers normally use bottled oxygen?

No. Supplemental oxygen is not routinely required for a properly paced Base Camp trek. It may be used during an emergency, but needing oxygen is not a reason to continue ascending.

Is Everest Base Camp safe?

Thousands of people complete the trek, but it cannot be described as risk-free. A gradual itinerary, competent guide, appropriate insurance and willingness to turn back make the journey safer. Start with our Everest Base Camp visitor guide if you need a clearer picture of the route and destination.