Nepal Outdoor Expeditions - Himalayan Trekking, Adventure Tours & Cultural Expeditions

Altitude sickness is the collective term for a spectrum of conditions your body can experience when it ascends to high altitude faster than it can physiologically adapt. At elevation, atmospheric pressure drops, which means each breath delivers fewer oxygen molecules to your lungs and bloodstream. Your body responds by increasing breathing rate, producing more red blood cells, and adjusting blood chemistry, a process called acclimatization. When you ascend too fast, this process cannot keep pace. Nepal is one of the most concentrated high-altitude trekking destinations on Earth. The Everest Base Camp trek crosses the Kongma La pass at 5,535 metres. The Annapurna Circuit summits Thorong La at 5,416 metres. Even the relatively moderate Langtang Valley trek reaches above 4,700 metres. For context, most trekkers arrive in Kathmandu (1,400 m) from sea level. The altitude gain over a two-week itinerary is dramatic. According to the Himalayan Rescue Association (HRA), roughly 75% of trekkers experience some form of altitude sickness above 3,000 metres in Nepal. Mild AMS is common and manageable. Severe AMS, HAPE, and HACE are less common but responsible for most altitude-related deaths in the Himalayas. Understanding the full spectrum is the single most important thing you can do before you set foot on the trail.

What are the Symptoms of Altitude Sickness: Mild, Moderate, and Severe

Knowing exactly what to look for and how to distinguish a bad headache from a medical emergency can be the difference between a successful trek and a life-threatening situation.

Mild AMS Symptoms

Mild AMS is common above 2,500 metres and usually resolves with rest and acclimatization. Do not ascend further until all symptoms have cleared.

Headache: the hallmark symptom; typically dull and persistent, often worse in the morning
Fatigue and weakness: disproportionate to the physical effort
Dizziness or light-headedness
Loss of appetite or nausea
Disturbed sleep: including frequent waking and strange breathing patterns (Cheyne-Stokes breathing)
Mild swelling in hands, feet, or face (peripheral edema)

The Lake Louise Score is a widely used field diagnostic tool. A score of 3 or more (with headache plus at least one other symptom) indicates mild to moderate AMS. Your guide should know this scoring system.

Moderate AMS Symptoms

If mild symptoms worsen or do not improve after 24 hours of rest at the same altitude, AMS is progressing. Do not ascend. Consider descending 300–500 metres.

Severe, persistent headache unresponsive to ibuprofen or paracetamol
Vomiting (not just nausea)
Extreme fatigue and weakness that limits normal activity
Shortness of breath at rest
Decreased urine output
Confusion or difficulty concentrating

Severe AMS / HACE Symptoms (Medical Emergency - Descend Immediately)

High-Altitude Cerebral Edema (HACE) is fluid accumulation in the brain. It is life-threatening and develops from untreated moderate AMS.

Severe confusion, disorientation, or irrational behaviour
Loss of coordination - the "walk the line" test (ask the person to walk heel-to-toe in a straight line; failure indicates HACE)
Extreme lethargy - difficulty staying awake
Loss of consciousness in advanced cases

Emergency Protocol: If HACE is suspected, descend immediately, administer dexamethasone if available, and arrange helicopter evacuation. Do not wait for morning. Do not wait for improvement.

HAPE Symptoms (Medical Emergency - Descend Immediately)

High-Altitude Pulmonary Edema (HAPE) is fluid accumulation in the lungs. It is the most common cause of altitude-related death in Nepal. It can occur without preceding AMS.

Severe shortness of breath at rest or with minimal exertion
Persistent dry cough that progresses to a wet, gurgling cough (sometimes producing pink or frothy sputum)
Extreme weakness - inability to walk without stopping
Cyanosis (bluish tint to lips or fingernails)
Crackling sounds in the lungs (detectable with a stethoscope)

Emergency Protocol: Descend a minimum of 1,000 metres immediately. Administer nifedipine if available. Use a portable hyperbaric chamber (Gamow Bag) if descent is impossible. Arrange helicopter evacuation urgently.

Who is at Risk? Key Risk Factors for AMS in Nepal

One of the most important and frequently misunderstood facts about altitude sickness is that physical fitness does not protect you. A marathon runner is just as susceptible to AMS as a first-time trekker. What matters is individual physiology, ascent rate, and prior acclimatization.

Factors That Increase Your Risk

Rapid ascent: the most significant controllable risk factor. Flying directly to Lukla (2,860 m) and pushing to Namche Bazaar without an extra rest day is a common mistake.
Previous history of AMS: if you have had it before, you are more likely to get it again. The reverse is also true: if you tolerated altitude well previously, you are likely to do so again.
Living at low altitude: people who live at sea level or near it have no baseline acclimatization advantage.
Dehydration: inadequate fluid intake worsens symptoms and may accelerate onset.
Alcohol and sedatives: both suppress breathing, reducing oxygen intake at night.
Overexertion: pushing hard physically at altitude increases oxygen demand before your body has adapted.
Age: younger trekkers (under 25) may actually be at slightly higher risk, possibly due to greater willingness to push pace.
Certain medical conditions: pre-existing anaemia, respiratory conditions, or cardiovascular disease increase risk. Consult your doctor before any high-altitude trek.
Starting altitude: if your trek begins above 3,500 m (e.g., flying into Jomsom for Upper Mustang, or Lukla for Everest routes), your body has less time to begin adapting.

Altitude Sickness Prevention: The Golden Rules

Prevention is far more effective than treatment. Every experienced Himalayan guide, trekking doctor, and expedition leader will tell you the same thing: the mountain will always be there. Your health will not fix itself at 5,000 metres.

Rule 1: Climb High, Sleep Low

This is the fundamental acclimatization principle. During the day, you can ascend higher than your sleeping altitude, but return to a lower camp to sleep. This stimulates acclimatization while giving your body recovery time. On the Everest Base Camp trek, the classic "rest day" at Namche Bazaar (3,440 m) with a hike to the Everest View Hotel (3,880 m) is a textbook application of this rule.

Rule 2: Follow the 300-500 Metre Rule

Above 3,000 metres, limit your sleeping altitude gain to 300–500 metres per night. Most commercial trekking itineraries are designed around this. If a guide or agency offers you a "faster" itinerary that skips acclimatization nights, treat it as a red flag.

Rule 3: Plan Rest Days (Non-Negotiable)

On any trek above 4,000 metres, rest days are not optional. Recommended rest days on major Nepal treks:

Trek	Recommended Acclimatization Stop(s)
Everest Base Camp	Namche Bazaar (2 nights), Dingboche or Pheriche (2 nights)
Annapurna Circuit	Manang (2 nights)
Manaslu Circuit	Samagaon (2 nights)
Langtang Valley	Kyanjin Gompa (2 nights)
Kanchenjunga	Multiple staged rest points above 3,500 m

Rule 4: Stay Hydrated

Drink 3-4 litres of water per day at altitude. Dehydration compounds altitude symptoms and is easy to prevent. Avoid alcohol for the first 48 hours at any new altitude above 3,000 metres. Caffeine in moderate quantities is fine and does not significantly worsen AMS.

Rule 5: Know Your Medication Options

Acetazolamide (Diamox) is the most widely used prophylactic medication for altitude sickness. It works by stimulating breathing, which increases blood oxygen levels and speeds up acclimatization. It is a prescription drug in most countries; obtain it before you leave home.

Dosage: 125-250 mg twice daily, beginning 1-2 days before ascent
Common side effects: Increased urination (carry it on, this is normal), tingling in fingers and toes, mild nausea
Allergy note: Diamox is a sulfonamide. People with sulfa drug allergies should not take it without consulting a physician.
Not a substitute for proper acclimatization: Diamox reduces risk; it does not eliminate it.

Dexamethasone is a steroid used for treatment of severe AMS and HACE, not routine prevention. Nifedipine is used in HAPE treatment. Carry these only if your guide or expedition doctor has briefed you on their use.

Rule 6: Listen to Your Body, and Your Guide

No summit, no teahouse, no social media achievement is worth your life. The Himalayan Rescue Association's mnemonic is worth memorising: "If in doubt, don't go up." Trust your guide's assessment. Experienced Nepali guides are trained to recognise AMS and will recommend rest or descent before symptoms become dangerous. Our guides at Nepal Outdoor Expeditions are HRA-certified and carry pulse oximeters on all high-altitude treks to monitor blood oxygen saturation in the field.

Altitude Sickness on Specific Nepal Treks

Everest Base Camp Trek

The Everest Base Camp (EBC) trek reaches 5,364 metres, and Kala Patthar, the popular viewpoint, sits at 5,644 metres. It is the most altitude-demanding of Nepal's "mainstream" treks. Critical altitude points:

Namche Bazaar (3,440 m): first major AMS risk point; 2-night stay mandatory
Tengboche (3,860 m): common headache night
Dingboche (4,410 m): 2-night acclimatization stay essential; day hike to Nangkartshang Peak (5,083 m)
Lobuche (4,940 m): HAPE and HACE cases reported regularly here
Everest Base Camp (5,364 m): oxygen saturation commonly drops to 75–85%

AMS incidence on EBC: Studies suggest 30-40% of trekkers experience mild AMS on the standard 12-14 day EBC itinerary. Cases of HAPE and HACE, though less common, occur every season. Helicopter rescues from the Khumbu region number in the hundreds each year. If you are planning the Everest Base Camp trek, choose a 14-day or longer itinerary. The extra days are not "padding"; they are physiological insurance.

Annapurna Circuit Altitude Sickness

The Annapurna Circuit is Nepal's most diverse trek, and Thorong La pass (5,416 m) is its crux. Trekkers must cross the pass in one day, ascending from Thorong Phedi (4,450 m) to the pass and descending to Muktinath (3,760 m). Critical altitude points:

Manang (3,519 m): 2-night acclimatization stop; the Himalayan Rescue Association runs a free altitude sickness clinic here
High Camp (4,925 m): optional overnight for an early start on the pass
Thorong La Pass (5,416 m): cross in one push; do not attempt if you have active AMS symptoms

Many trekkers push too fast on the lower circuit (Besisahar to Manang) and arrive at Manang already mildly affected. The road in the lower valley enables faster progress, which can tempt trekkers to skip nights. Resist this. The HRA clinic in Manang offers free health checks and altitude talks. Attend it. The doctors have assessed thousands of trekkers and can tell you with reasonable accuracy whether your body is ready for Thorong La. Our Annapurna Circuit trek packages include dedicated acclimatization days at Manang and are designed with Thorong La success as a primary planning consideration.

Other High-Altitude Treks

Manaslu Circuit: Crosses Larkya La (5,106 m). Less crowded than EBC with fewer rescue resources, acclimatization discipline is even more important.

Kanchenjunga: Remote, above 5,000 m for multiple days. Requires careful itinerary planning and experienced guides with wilderness first aid training.
Three Passes Trek: Crosses three passes above 5,300 m (Renjo La, Cho La, Kongma La). Extended time at extreme altitude.
Upper Mustang: Begins at Jomsom (2,720 m) but Lo Manthang sits at 3,840 m. The rapid gain from a short flight is the risk factor here.

Altitude Sickness Treatment: What to Do When Symptoms Strike

Despite perfect preparation, AMS can still occur. Here is the field treatment protocol your guide will follow, and what you should know as a trekker.

Step 1: Stop Ascending Immediately

The moment you recognise AMS symptoms (headache, nausea, fatigue), stop. Do not attempt to "sleep it off" at altitude and continue ascending the next morning unless symptoms have completely resolved.

Step 2: Rest at the Same Altitude

For mild AMS, resting for 24 hours at the same altitude is often sufficient. Take paracetamol (1,000 mg) or ibuprofen (400–600 mg) for headache. Drink fluids. Avoid alcohol and sleeping tablets.

Step 3: Descend if Symptoms Do Not Improve

If mild symptoms persist for more than 24 hours or worsen, descend 300–500 metres. Even a modest descent often produces rapid improvement. This is the single most effective treatment available on the trail.

Step 4: Administer Diamox Therapeutically

Diamox can also be used therapeutically (not just preventively) at 250 mg twice daily. It is most effective for mild to moderate AMS.

Step 5: Emergency Descent + Evacuation for HACE/HAPE

For any suspected HACE or HAPE: descend immediately, regardless of time of day or weather. Use a Gamow Bag if descent is not immediately possible. Administer:

HAPE: Nifedipine 30 mg extended-release (or 10 mg immediate-release every 4–6 hours), supplemental oxygen if available
HACE: Dexamethasone 8 mg initial dose, then 4 mg every 6 hours

Contact your travel insurance provider and arrange helicopter evacuation. Most policies cover rescue from altitude; confirm this before you leave home.

How Nepal Outdoor Expeditions Keeps You Safe at Altitude

At Nepal Outdoor Expeditions, altitude safety is built into every aspect of how we design and operate high-altitude treks. Our guides are graduates of the Himalayan Rescue Association's training programs and carry pulse oximeters on all treks above 3,000 metres. We monitor oxygen saturation readings at each camp and make conservative decisions based on data, not optimism. Our itineraries are built around medically recommended acclimatization profiles, not the minimum days needed to complete the route. On treks like Everest Base Camp and the Annapurna Circuit, we include mandatory rest days at key altitude thresholds and use the "climb high, sleep low" principle wherever the route allows. We provide comprehensive pre-trek altitude briefings, carry basic emergency medications (including dexamethasone and nifedipine), and maintain direct communication with helicopter rescue operators throughout the trekking season. If you need to descend, we move quickly. Explore our guided trekking packages designed with your safety at altitude as the foundational principle.

Final Word: Altitude Is a Partner, Not an Enemy

Altitude sickness is not a reason to avoid Nepal's high-altitude treks; it is a reason to respect them. With sound planning, a properly paced itinerary, attentive guides, and the knowledge to recognise and respond to symptoms, millions of trekkers reach their goals each year. The Khumbu Icefall, Thorong La at sunrise, the first unobstructed view of Annapurna South- these rewards are absolutely achievable. The difference between a safe, successful trek and a medical emergency almost always comes down to preparation and the willingness to slow down. Build your itinerary around acclimatization, not deadlines. Choose an operator who takes altitude safety seriously, then enjoy every step of your journey. Explore Nepal Outdoor Expeditions' full range of high-altitude trekking packages and speak with our team about building an itinerary that gives your body the time it needs.

Frequently Asked Questions

What is the first sign of altitude sickness while trekking in Nepal?

A persistent headache is the earliest and most reliable warning sign. It typically appears 6-12 hours after arriving at a new altitude and is often worst in the morning. If you develop a headache above 2,500 metres, rest at the same altitude and do not ascend until it clears completely.

Can I prevent altitude sickness with medication alone?

No, Acetazolamide (Diamox) reduces your risk of developing AMS and can speed acclimatization, but it is not a replacement for a proper acclimatization schedule. Trekkers who take Diamox and still ascend too fast can still develop AMS. The medication works best alongside, not instead of, a gradual ascent profile.

Does fitness level affect altitude sickness risk?

Physical fitness does not protect you from altitude sickness. Altitude response is primarily a matter of individual physiology and acclimatization rate. Highly fit athletes can and do develop severe AMS. Maintaining a steady pace (not racing up the trail) is more relevant than your VO₂ max.

How high is Everest Base Camp and at what altitude does sickness become a concern?

Everest Base Camp sits at 5,364 metres. Altitude sickness risk increases progressively above 2,500 metres and becomes a significant concern above 3,500 metres. On the standard EBC route, the first major acclimatization checkpoint is Namche Bazaar (3,440 m), where a two-night stay is medically recommended.

What should I do if I feel sick at altitude and my guide wants to continue?

You have the right, and the responsibility, to stop. No guide should pressure a trekker to continue when they are experiencing AMS symptoms. If you are trekking with Nepal Outdoor Expeditions, your guide is trained and instructed to respect your medical status over any schedule pressure. If you ever feel your guide is underreacting to symptoms, use the "STOP" rule: Stop, Think, Observe, Plan, and if in doubt, return.

What is the difference between AMS, HAPE, and HACE?

Acute Mountain Sickness (AMS) is the general altitude illness syndrome: headache, fatigue, nausea, poor sleep. High-Altitude Cerebral Edema (HACE) is a severe form where fluid accumulates in the brain, causing confusion and loss of coordination. High-Altitude Pulmonary Edema (HAPE) is fluid in the lungs, causing breathlessness and a wet cough. HAPE is the most common cause of altitude-related death. Both HACE and HAPE are medical emergencies requiring immediate descent and evacuation.

Can children trek at high altitude in Nepal?

Children can trek at altitude with careful planning and conservative acclimatization. However, they may be less able to articulate symptoms clearly. Paediatric altitude sickness research is limited; most HRA physicians recommend keeping children below 3,500 metres unless they have prior high-altitude experience. Consult a travel medicine specialist before planning a high-altitude trek with children.

Altitude Sickness on Nepal Treks: Symptoms, Prevention, and What to Do