Everest Base Camp Altitude Sickness Guide: Symptoms, Prevention & Safety Tip

What Is Altitude Sickness on Everest Base Camp

Altitude sickness (or Acute Mountain Sickness) occurs when you do not have enough oxygen in your body due to the altitude at which you are hiking.

The air we breathe at sea level has an approximate oxygen content of approximately 21%. That percentage of oxygen remains constant at all altitudes. However, the air pressure changes as we go up in altitude. The higher up you go, the less air pressure there is and therefore the less oxygen that can be inhaled and used by the body. Your body tries to adjust to the low amount of oxygen received by your lungs, which struggle to adjust to using less oxygen, and this can cause symptoms like headaches, nausea, shortness of breath, etc., of altitude sickness.

AMS can start to occur at elevations as low as 2,500 metres above sea level, and the risk of experiencing AMS continues to increase as trekkers climb Everest Base Camp Trek altitude from Lukla (2,860 metres) to Everest Base Camp (5,364 metres) and now to Kala Patthar (5,644 metres). Most of the time, trekkers who hike above 4,000 metres will experience some degree of altitude-induced discomfort, regardless of their level of fitness and preparation for their trek.

Important to understand: AMS is not a weakness. Rather, it is a naturally occurring physiological response of the body that occurs when the body travels to a higher altitude without enough time to adapt to its new environment. So the solution to AMS is usually just to give the body adequate time to adjust to the new altitude, not to try to exert more physical effort.

If symptoms of altitude sickness go untreated and you continue to ascend, altitude sickness can progress to very serious and possibly fatal conditions (HACE and HAPE). Don't ignore altitude sickness symptoms while at altitude.

Common Symptoms of Altitude Sickness

Altitude sickness has 3 levels of severity. So to treat it, you must be familiar with the different levels in order to provide the appropriate level of response. Identifying which level of altitude sickness you or one of your fellow trekkers has is the most important skill to possess on the trail.

Mild AMS: What It Feels Like

Many people experience a mild, constant headache upon arrival in Namche Bazaar (3,440 metres). It's the most frequent early sign of altitude sickness along the EBC route. Many times, the headache worsens when bending or moving rapidly. Other symptoms of mild altitude sickness include a nauseous feeling, exhaustion after minimal exertion, and frequent interruptions during sleep.

If you have mild symptoms, the best thing to do is wait a few days at the same altitude and let your body adjust. Drink lots of water and don't move on to the next higher altitude until all mild symptoms are gone. Too many trekkers think they can simply work through altitude sickness symptoms and keep moving higher. This doesn't work and will often result in serious problems. Don't make that mistake.

Moderate AMS: When to Stop

If your headache isn't improving even with rest and hydration, if you're vomiting, and if you're feeling dizzy while resting, you're experiencing moderate altitude sickness. At this point, don't continue to a higher altitude. Stay at the same altitude or go down 300 to 500 metres to help your body recover. Moderate altitude sickness can greatly affect your Everest Base Camp Trek difficulty experience on the trail and can make easy trails feel at least moderately difficult or challenging.

Severe AMS: HACE and HAPE

HACE (high-altitude cerebral edema, swelling or accumulation of fluid in the brain) and HAPE (high-altitude pulmonary edema, accumulation of fluid in the lungs) are potentially fatal conditions. One of the most recognizable symptoms of HACE is loss of coordination. If you can't walk in a straight line, that's a medical emergency.

Extreme breathlessness at rest may indicate HAPE, the accumulation of fluid in the lungs. Both of these conditions are life threatening and require immediate descent. Don't wait for morning and don't try a second day of rest. You must descend now. If you or someone in your party exhibits HACE or HAPE symptoms, descend immediately. Each 100 metres of vertical distance you descend may save a life.

Why Altitude Sickness Happens on the EBC Trek

The EBC Trek has a drastic altitude gradient over a short overall length of time. You begin with a flight into Lukla at 2,860 metres (9,383 feet) and in approximately 9 to 10 days reach EBC at 5,364 metres (17,590 feet). This equates to almost 2,500 metres (8,200 feet) in 14 days. Your body will need time to produce more red blood cells, increase lung capacity, and make changes in breathing patterns. When the ascent is quicker than the body's adaptive process, altitude sickness may occur.

Three factors make the EBC trek particularly difficult regarding altitude. First, you gain a considerable amount of altitude from a cumulative standpoint and there are no long flat sections for your body to get a real rest. Second, you experience multiple large altitude gains in a single day of trekking. Third, as you gain altitude, your sleep quality deteriorates, so your body takes longer to recover from one day to the next.

The safest way to acclimatize is by trekking the Everest Base Camp Trek route on a properly set out itinerary with sufficient acclimatization days. The number one risk factor for serious altitude sickness on this trek is skipping rest days to save time. 

Our team's rule: Our rule is simple. If someone has symptoms of altitude sickness, they don't go any further until they rest and feel completely normal, not just a little better.

How to Prevent Altitude Sickness

Prevention is more effective than treatment. Our guides incorporate all of these habits every day from the very beginning of your trek. So by using them consistently, you're much less likely to develop altitude sickness.

Do This

• Ascend slowly. Don't gain more than 300 to 500 metres of sleeping altitude each day when above 3,000 metres.
• Take rest days and scheduled acclimatization days in Namche and Dingboche. They're built into your itinerary for your safety.
• Drink 3 to 4 litres every day. Hydration helps your blood carry oxygen more effectively.
• Eat warm, calorie-rich meals regularly. You burn more calories to stay warm and function at high altitude.
• Walk slowly and breathe deeply. A pace where you can comfortably converse is just right for this trek.
• Sleep at a lower altitude than you climbed during the day. Use the climb high, sleep low concept.
• Communicate with your guide immediately if you experience any symptoms. Early communication helps you avoid small issues becoming larger ones.

Avoid This

• Never skip acclimatisation days, even if you feel fine. Acclimatisation is a process, and each person's pace is unique.
• Never drink alcohol above 3,500 metres. It's a dehydrating agent and will inhibit your body's ability to recover through restorative sleep.
• Never use sleeping pills at high elevation. They suppress the amount of oxygen you get while sleeping and hinder your ability to acclimatise.
• Never ascend if you have a headache. On the ascent, a headache is your body telling you to stop and rest.
• Don't rush. Moving too quickly and ascending rapidly causes a rapid increase in heart rate and oxygen demand.

From our guides:  Proper Everest Base Camp Trek acclimatisation is the most important factor for a successful trek. No level of fitness, no medication, and no amount of determination can make up for not taking the required rest days to allow for proper acclimatisation.

Best Acclimatisation Plan for Everest Base Camp

A good itinerary integrates acclimatization into your trip on its own. The standard 14-day EBC itinerary incorporates two critical rest days: one in Namche Bazaar and a second at Dingboche. The daily acclimatisation hike up and down 600 meters also uses the climb high, sleep low principle. Here's how this works through the important days.

Why Namche Bazaar Matters Most

In Namche, at 3,440 metres, many trekkers start noticing the first symptoms of altitude sickness on their very first night. The second day of rest isn't just a comfort day. It's a physiological necessity. The acclimatisation hike above Namche takes you to about 3,800 metres, and then you sleep at 3,440 metres. This difference in elevation causes your body to produce more red blood cells. You'll feel the benefit of it higher up.

Why Dingboche Is the Second Key Stop

Dingboche is the last major village at 4,410 metres along the route to Everest Base Camp, and beyond it, the terrain becomes very difficult. When acclimatising here, you'll go on hikes that reach altitudes above 5,000 metres and return to 4,410 metres. Returning to Dingboche after a 5,000-metre hike will enhance your body's ability to reach Base Camp and climb Kala Patthar.

Planning tip: A good Everest Base Camp Trek Itinerary 14 Days includes both Dingboche and Namche Bazaar as two-day rest stops. If an itinerary doesn't include either of these rest days, it's too short. Don't cut corners here.

Safety Tips and What to Do in an Emergency

Altitude sickness can occur even if you plan well and pace your trek properly. So knowing what to do and reacting quickly can determine whether it's manageable or a serious condition.

When to Descend

• If you lose coordination and can't walk in a straight line (HACE), go down at once.
• If you can't breathe at rest, cough a great deal, or have blue lips (HAPE), go down at once.
• If your headache hasn't responded after 12 to 24 hours of rest, drinking lots of water, and over-the-counter pain relief, it may be time to go down.
• Never go up until you have no symptoms of AMS, even if you think they're minor.

Diamox: The Basics

Diamox (Acetazolamide) is widely used for AMS prevention and treatment. It speeds up your breathing rate and improves the processing of oxygen at altitude. Your doctor should discuss the use of Diamox with you before you go trekking, as it's a prescription drug.

Some trekkers take it as a preventative measure before going above 2,500 metres, and some wait until they actually start experiencing symptoms. Common side effects include an increased need to urinate, tingling of the extremities, and an altered taste for soda. If you've had a reaction to sulfa drugs, don't take Diamox.

Diamox doesn't cure altitude sickness. It will only help relieve the symptoms. So if you have any severe symptoms, go down immediately regardless of whether or not you've taken Diamox.

Helicopter Rescue

If you're trekking in the Khumbu region of Nepal, helicopter evacuation services can get you to safety quickly. With clear weather, you can fly to support villages within a few hours. After contacting the rescue service through your guide, the helicopter will fly to a designated landing area and take you to the hospital in Kathmandu.

Helicopter rescues range from $3,000 to $6,000 USD. So travel insurance is essential. Every trekker should have an insurance policy that clearly states it covers high altitude trekking at or above 5,000 metres and helicopter retrieval. Don't rely on personal funds for this as emergency rescue can increase your Everest Base Camp Trek Cost dramatically.

Insurance tip:  Read the fine print of your travel insurance before you depart. Standard travel insurance won't cover trekking above 4,000 metres. You must purchase a specialist high altitude policy.

Who Should Avoid or Be Extra Careful

Altitude sickness has nothing to do with your level of fitness. An elite athlete can get it, and an unfit trekker may not. But certain groups should prepare thoroughly and consult their doctor before attempting this trek.

Beginners and First-Time Trekkers

First-time trekkers should choose a 14-day itinerary instead of a faster one and not try to accelerate the pace. Talk to your guide frequently about pacing. The mountain doesn't reward speed. It rewards patience. So choose the best time for the Everest Base Camp trek: spring or autumn, for the most stable weather.

Individuals with chronic health conditions are advised to seek medical clearance before beginning their EBC trek.

People With Pre-Existing Health Conditions

• Heart condition: High altitude increases heart rate and blood pressure. So consult a cardiologist before attempting the EBC trek.
• Lung condition: Asthma, COPD, and other lung conditions are worsened by high altitude, and medical clearance is needed.
• Anaemia: A low red blood cell count means your body already doesn't have enough oxygen, and high altitude reduces it further.
• Pregnant women should not attempt to trek at high altitude due to the lack of oxygen available for both the mother and the unborn baby.
• Previous history of altitude sickness: If you've suffered from altitude sickness before, you're statistically more likely to experience it again. So discuss with your physician whether you should take Diamox as a preventative measure before your EBC trek.

Older Trekkers

Completing the EBC trek is possible for older trekkers. Many of our trekkers have successfully trekked to Base Camp at age 60 and above, even into their 70s. The main differences are preparation, pacing, and consulting with your doctor. A conservative ascent profile with a slower incremental elevation increase may benefit a majority of older trekkers. Plus, additional rest days between major altitude gains should be allowed when planning the trek.

Children

A child's body reacts differently from an adult's body to altitude. So the development of symptoms and their recognition can be quick and difficult to spot in children. Medical professionals typically don't recommend taking children under 10 years of age above 3,500 metres. If you have older children, consult with a doctor who has experience with high altitude medicine before planning your trek.

Final advice from our team: If you have any doubts regarding your physical readiness for this trek, please refer to our Everest Base Camp difficulty guide and consult with a doctor who specialises in high altitude or travel medicine. It's important to have as much information as possible before making your decision.

 Every year, thousands of trekkers successfully arrive at Everest Base Camp, not because they were fitter than everyone else or more experienced. They made it because they respected the mountain, listened to their bodies, and followed a reasonable plan. It's the same approach our team incorporates in every trek we guide.