Altitude Sickness on Nepal Treks — Complete Prevention and Safety Guide 2026

Altitude sickness is the single biggest health risk on any Himalayan trek. Not injury. Not weather. Not the food. Altitude.

I've been guiding treks in Nepal since I was a teenager. My father guided before me, and my grandfather before him. In all that time, we've never had a serious altitude incident on our treks. That's not luck — it's preparation, experience, and knowing when to turn around.

Here's everything you need to know about altitude sickness before you trek in Nepal.

What is altitude sickness?

Altitude sickness — also called Acute Mountain Sickness (AMS) — happens when your body doesn't have enough time to adjust to lower oxygen levels at high elevation. The higher you go, the less oxygen there is in each breath. Your body needs time to adapt.

Most people start feeling altitude effects above 2,500m. Serious symptoms usually appear above 3,500m. The risk increases significantly above 4,000m.

AMS can affect anyone. It doesn't matter how fit you are, how old you are, or how many mountains you've climbed before. There's no reliable way to predict who'll get it. I've seen marathon runners struggle at 4,000m while 60-year-old first-time trekkers sail through to 5,000m.

The symptoms — know them

Mild AMS (common above 3,000m):

• Headache (the most common first symptom)
• Nausea or loss of appetite
• Tiredness beyond normal fatigue
• Dizziness
• Difficulty sleeping

These are your body's warning signals. Mild AMS is manageable if you respond correctly.

Severe AMS (medical emergency):

• Headache that doesn't respond to painkillers
• Persistent vomiting
• Confusion or disorientation
• Loss of coordination (ataxia) — if you can't walk in a straight line, it's serious
• Breathlessness at rest
• Gurgling sound when breathing (fluid in the lungs — this is HACE or HAPE)

Severe AMS can develop into two life-threatening conditions:

• HACE (High Altitude Cerebral Edema) — fluid on the brain
• HAPE (High Altitude Pulmonary Edema) — fluid in the lungs

Both can kill within hours if untreated. The treatment is the same in both cases: descend immediately.

The golden rule: ascend slowly

The single most effective way to prevent altitude sickness is to gain altitude gradually. Your body needs time to produce more red blood cells and adjust to lower oxygen.

The standard guideline:

• Above 3,000m, don't increase your sleeping altitude by more than 300–500m per day
• Take a rest day every 1,000m of altitude gained
• "Climb high, sleep low" — it's fine to hike up to a viewpoint during the day as long as you come back down to sleep

This is exactly how our itineraries are designed. On the Everest Base Camp trek, we build in acclimatisation days at Namche Bazaar (3,440m) and often at Dingboche (4,410m). These aren't wasted days — they're the reason you'll make it to Base Camp feeling strong rather than sick.

What our guides do

Every guide trained by The Everest Holiday follows a strict altitude safety protocol:

Twice-daily oxygen checks.

Our guides carry a pulse oximeter — a small device that clips onto your finger and measures your blood oxygen saturation (SpO2). We check every trekker's levels in the morning and evening. A healthy reading at altitude is generally above 80% SpO2. If your levels drop or your resting heart rate spikes, we take action before symptoms get worse.

Daily symptom assessment.

Each morning, your guide will ask how you slept, whether you have a headache, and how your appetite is. These aren't casual questions — they're part of a systematic check based on the Lake Louise Acute Mountain Sickness scoring system.

Immediate descent if needed.

If a trekker shows signs of moderate to severe AMS, we descend. No discussion, no "let's wait and see." We've never had a serious incident because we don't gamble with altitude. I'd rather you come back healthy than reach Base Camp sick.

Hydration reminders.

Dehydration makes altitude sickness worse. Our guides will remind you to drink 3–4 litres of water per day at altitude. It sounds like a lot. It's not.

Acclimatisation days — why they matter

Some trekkers see "rest day" on the itinerary and think it's wasted time. It's the opposite — it's the most important day of your trek.

On an acclimatisation day in Namche Bazaar, for example, you'll hike up to the Everest View Hotel at about 3,880m, spend a couple of hours enjoying the views, then walk back down to sleep at 3,440m. This "climb high, sleep low" approach trains your body to handle altitude more efficiently.

Companies that skip acclimatisation days to offer a cheaper, shorter trek are cutting the one thing that keeps you safe. Don't fall for it.

Medication

Diamox (Acetazolamide) is the most commonly used medication for altitude sickness prevention. It's a prescription drug that speeds up acclimatisation by making you breathe faster and more deeply.

Some trekkers take it preventatively from about 2,500m onwards. Others carry it and only use it if symptoms appear. Talk to your doctor before your trip — not your trekking company — about whether Diamox is right for you.

Common Diamox side effects: tingling in your fingers and toes, increased urination, and carbonated drinks tasting flat. These are annoying but harmless.

Ibuprofen can help with altitude headaches. Paracetamol works too. But if painkillers aren't touching the headache, that's a warning sign — tell your guide.

Helicopter evacuation

If things get serious, helicopter evacuation is available throughout the Everest and Annapurna regions. A helicopter can reach most trekking areas within a few hours of being called.

This is why travel insurance is mandatory for our treks. Your insurance must cover:

• Helicopter rescue and evacuation
• Altitude up to 6,000m
• Medical treatment and hospitalisation

Without insurance, a helicopter evacuation can cost $3,000–$5,000 or more. With insurance, it's covered. Do not trek in Nepal without proper insurance. We check every trekker's policy before departure.

Things that make altitude sickness worse

• Alcohol. Seriously, don't drink above 3,000m. That celebratory beer in Namche can wait until you're back in Kathmandu.
• Dehydration. Drink water constantly. If your urine isn't clear, you're not drinking enough.
• Pushing through symptoms. This is the big one. Pride kills people at altitude. If you feel terrible, say something. Your guide needs to know.
• Sleeping pills. They suppress your breathing at night, which is the last thing you want at altitude. Avoid them entirely above 3,000m.
• Ascending too fast. Sticking to the schedule matters. Don't try to "get ahead" by skipping to the next village.

What to do if you feel symptoms

• Tell your guide immediately. Don't tough it out.
• Stop ascending. Stay at your current altitude or go down.
• Hydrate. Drink water or warm tea.
• Take painkillers for headache if appropriate.
• Rest. Your body is telling you something — listen.
• If symptoms don't improve in 4–6 hours, descend 500m. This usually brings rapid relief.
• If symptoms are severe (confusion, loss of coordination, difficulty breathing at rest), descend immediately and arrange evacuation if necessary.

Descending just 500–1,000m can make a dramatic difference. Altitude sickness almost always improves when you go lower.

Training before your trek

You don't need to be an athlete, but preparing your body helps:

• Walk hills for 4–6 hours regularly in the 2–3 months before your trek
• Build cardiovascular fitness (running, cycling, swimming all help)
• Practice walking with a loaded daypack
• If you live near mountains, do some altitude hikes

The fitter you are, the more energy you'll have to enjoy the trek. Fitness doesn't prevent AMS, but it means your body handles the physical effort better, leaving more energy for acclimatisation.

The bottom line

Altitude sickness is serious but manageable. With proper acclimatisation, an experienced guide, and the willingness to listen to your body, the vast majority of trekkers reach their goal safely.

My family has been guiding people through these mountains for over sixty years. The Himalayas are magnificent, but they demand respect. We make sure every trekker who walks with us understands that — and comes home healthy.

If you've got questions about altitude, fitness, or preparation for your trek, reach out. I'm happy to help you plan.

Ready to experience Nepal for yourself?

The Everest Holiday has guided trekkers through the Himalayas for over a decade with a near-perfect five-star TripAdvisor rating.

Browse our Nepal treks: www.theeverestholiday.com

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