Altitude Sickness: Prevention Guide for Himalayan Treks

What Is Altitude Sickness, Really?

Your body needs time to adjust to thinner air. When you climb faster than it can keep up, usually somewhere above 2,500 to 3,000 meters, your body starts sending warning signs. The Himalayan Rescue Association, which has run medical posts on the Everest and Annapurna trails since the 1970s, notes that AMS can actually begin as low as 2,300 meters. That's worth remembering if you're flying into Lukla for the EBC trek or starting the Langtang Trek, since you can be at that altitude within your first day or two.

If it's ignored, mild AMS can turn into something much more serious:

• HAPE (High Altitude Pulmonary Edema), fluid building up in the lungs

• HACE (High Altitude Cerebral Edema), fluid building up in the brain

Both need immediate descent and medical attention. Neither is something to push through.

Symptoms Worth Paying Attention To

• A headache that doesn't go away with rest or water

• Nausea or not wanting to eat

• Feeling unusually dizzy or wiped out, more than the day's walk should explain

• Trouble sleeping

• Getting short of breath even while sitting still

Here's the rule that actually matters: if symptoms are getting worse instead of better after resting, stop going up. If they don't improve, go down.

How to Actually Prevent It

Go slow, on purpose. The HRA recommends gaining no more than 300 to 500 meters of sleeping altitude a day once you're above 3,000m, with a rest day roughly every 1,000m. This is exactly why treks like Everest Base Camp and the Manaslu Circuit build in extra nights at places like Namche Bazaar. Those aren't lazy days. They're the reason most people finish the trek.

Climb high, sleep low. On acclimatization days, it actually helps to hike up higher during the day and come back down to sleep. Your body handles the adjustment better that way.

Drink more water than feels necessary. Somewhere around 3 to 4 liters a day. The air up there is dry, you lose fluid faster than you'd think, and dehydration makes AMS symptoms worse and harder to tell apart from the real thing.

Skip the alcohol and sleeping pills. Both slow your breathing down while you sleep, which is the last thing you want when your body's already working hard to get enough oxygen.

Ask a doctor about Diamox (acetazolamide) before you go. A lot of trekkers use it to help their bodies acclimatize faster, especially on tighter itineraries or big passes like Thorong La on the Annapurna Circuit or the high passes on the Everest Three Passes Trek. It's not something to start on the trail without talking to someone first.

Pick an itinerary that gives you time. This one's fully in your control. A rushed 10 day EBC trip is a very different risk than a well paced 15 day one with proper rest days at Namche and Dingboche. If you're weighing your options, our Annapurna Base Camp vs Everest Base Camp guide covers how the altitude and pacing compare.

Trek with a guide who's done this a hundred times. Someone who's spent seasons on these trails will usually catch early AMS symptoms before you do, and knows the difference between "you're fine, keep going" and "we need to head down now."

Which Treks Carry the Most Altitude Risk?

• Everest Base Camp Trek, topping out at 5,364m

1. Everest Three Passes Trek, crossing three passes above 5,300m

2. Annapurna Circuit, over Thorong La at 5,416m

3. Manaslu Circuit Trek, over Larkya La at 5,106m

4. Mera Peak and Island Peak, both above 6,000m and needing the most careful acclimatization schedule of all
   
   If you're newer to trekking or a bit nervous about altitude, routes like the Mardi Himal Trek or Langtang Trek sit lower and carry noticeably less risk, without giving up much of the scenery.

The Bottom Line

Altitude sickness isn't a fitness problem. Marathon runners get it just as often as first time trekkers, sometimes more often, because they're used to pushing through discomfort. It comes down to pace, water, and actually listening to how your body feels each morning. A good itinerary with real acclimatization days built in is the best protection you have, which is why we plan our treks around HRA recommended ascent rates instead of squeezing them into the shortest possible schedule.

Not sure which itinerary fits your pace or experience level? Get in touch with our team and we'll help you figure out the right one.