Everest Base Camp Altitude Sickness: What to Actually Watch For

Altitude sickness is the single most serious risk on this trek — and the most preventable one, which is what to actually watch for here rather than the fear itself. The route reaches 5,545m at Kala Patthar, with two nights spent above 5,000m. At that height, your body is running on reduced oxygen, and Acute Mountain Sickness can develop in anyone — fitness, age, and prior experience don’t protect you the way people assume. Here’s the good news: our 12-day itinerary is built specifically to minimise this risk — two acclimatisation days, a gradual ascent profile, and a strict no-ascent-with-AMS policy that we don’t bend for anyone. Trekkers who understand the symptoms, follow the prevention protocol, and report problems early consistently reach Kala Patthar safely.

Here’s what’s covered below:

• What Altitude Sickness Actually Is
• Symptoms by Severity
• Prevention That Actually Works
• Diamox — Should You Take It?
• Acclimatisation Schedule
• When to Descend
• FAQs

What It Is and Why It Happens

Altitude sickness — medically called Acute Mountain Sickness, or AMS — happens when your body ascends faster than it can adapt to the reduced oxygen up high. Above 2,500m, every 100m you climb cuts available oxygen by roughly 0.5%. At Gorak Shep (5,160m), you’re breathing in about 53% of the oxygen you’d get at sea level. That drop triggers a cascade in your body — faster breathing, a raised heart rate, and if the ascent happens too quickly, fluid retention in the brain and lungs that causes the actual symptoms of AMS. This isn’t a sign of weakness or poor fitness. It’s a straightforward physiological response, and it hits fit and unfit trekkers roughly equally once the ascent rate outpaces what the body can handle.

Who actually gets it

Anyone climbing to altitude can develop AMS. Prior high-altitude experience lowers the risk but doesn’t eliminate it. Fitness doesn’t protect you either — in fact, being very fit can sometimes raise your risk, because fit trekkers tend to push pace, which cuts into the acclimatisation time your body actually needs. There’s no reliable way to predict who’s susceptible before you’re already up there. The only real protection is following the acclimatisation schedule regardless of how strong you feel, drinking consistently, and telling your guide about symptoms the moment they show up instead of hoping they’ll pass by morning.

Symptoms by Severity

Mild AMS — common and manageable

Symptom	When It Typically Shows Up	What to Do
Headache	First night above 3,000m, often at Namche or Tengboche	Paracetamol + 500ml water, report if it doesn’t clear in 2 hours
Fatigue beyond expected effort	Above 3,500m, normal at that altitude	Rest and hydrate, don’t push pace
Reduced appetite	Consistently above 4,000m	Eat anyway, especially carbs
Disturbed sleep	Above 3,500m, especially the first few nights	Normal on its own, not a concern by itself
Mild dizziness on exertion	Above 4,000m on steep sections	Slow down, rest until it passes

Moderate AMS — report this immediately

Symptom	What It Means	What to Do
Persistent headache that paracetamol and water don’t clear within 2 hours	AMS is progressing, don’t ascend	Report to your guide, rest at current altitude
Nausea or vomiting	A moderate AMS indicator	Report immediately, no further ascent until it resolves
Breathlessness at rest	Concerning above 3,500m	Report immediately, descent may be necessary
Severe fatigue that doesn’t match your effort	Your body is genuinely struggling with the altitude	Rest day, reassess before going any higher

Severe AMS — this is an emergency, descend immediately

Symptom	Condition	What to Do
Loss of coordination or balance (ataxia)	HACE — High Altitude Cerebral Edema	Descend immediately, don’t wait until morning
Confusion or altered behaviour	Also a HACE indicator	Emergency descent, helicopter if needed
Persistent cough with pink or frothy sputum	HAPE — High Altitude Pulmonary Edema	Emergency descent, helicopter immediately
Severe breathlessness at rest	Also a HAPE indicator	Emergency descent, don’t wait

HACE and HAPE are life-threatening, full stop. The only correct response to either is immediate descent — not medication, not “let’s see how it looks in the morning.” Our guides carry pulse oximeters on every departure and monitor oxygen saturation above 4,000m. Any reading below 75% at altitude triggers an immediate medical assessment and, if needed, descent — no debate, no waiting to see.

Prevention Protocol — What Actually Works

Hydration: the single most effective thing you can do

Drink 3-4 litres of water every single day from Namche (3,440m) onward, no exceptions. Altitude suppresses your thirst — you genuinely won’t feel like drinking that much, but your body needs it regardless of what your thirst is telling you. Dehydration speeds up AMS symptoms significantly, and it’s the most easily preventable factor in the whole equation. Set yourself a deliberate schedule: 500ml by mid-morning, 500ml by lunch, 500ml by mid-afternoon, 500ml by evening. This one habit alone prevents most of the AMS headaches people get on this route.

Pace: walk slower than you think you need to

The most common trigger for AMS on EBC is walking too fast on the lower trail. Trekkers who feel strong at 2,500-3,000m tend to push their pace, and that accumulated altitude stress shows up two nights later as symptoms at Tengboche or Dingboche. The right pace above 3,000m is conversational — you should be able to say a full sentence without gasping for breath. Our guides enforce this from Lukla onward, and yes, we’ll ask fast-moving trekkers to slow down. That’s not us being cautious for the sake of it, that’s the actual protocol working.

The acclimatisation days: genuinely non-negotiable

The Day 3 hike above Namche (to roughly 3,900m) and the Day 6 hike to Nagarjun Hill (roughly 5,100m) are the physiological foundation the whole expedition rests on. Both follow “climb high, sleep low” — the most effective altitude adaptation tool available inside a 12-day schedule. Skipping either one in favour of an easier rest day removes the exact altitude stimulus your body needs to actually produce more red blood cells. Both days stay non-negotiable in our itinerary, and no amount of group pressure or schedule urgency changes that.

Diamox — Should You Take It?

Acetazolamide, better known as Diamox, is a prescription medication that speeds up acclimatisation by stimulating your breathing rate. It’s effective, widely used, and recommended by many wilderness medicine organisations for altitude above 3,000m.

Whether to take it is a medical and personal decision. Side effects can include increased urination, tingling in your hands and feet, and occasional nausea — not serious for most people, but uncomfortable enough to notice. Diamox doesn’t eliminate AMS risk, it reduces it. It’s also not a substitute for the acclimatisation days or the hydration protocol above — it works alongside them, not instead of them. Talk to your doctor about it at home, at least 4 weeks before departure, not in Kathmandu on arrival day when it’s too late to see how your body responds to it.

Who tends to benefit most

Trekkers with a history of AMS on previous trips, anyone ascending quickly from sea level, and anyone whose doctor recommends it after reviewing their cardiovascular health. Some trekkers choose to carry it as rescue medication instead of taking it preventively — only starting it if symptoms actually develop above Namche. The right approach genuinely varies by person, and your doctor is the one who should make that call, not a trekking blog.

Acclimatisation Schedule

Day	Overnight	Altitude	What’s Happening
Day 1	Phakding	2,610m	Short day, your body adjusts to the Lukla altitude jump
Day 2	Namche	3,440m	First major altitude gain, first night above 3,000m
Day 3	Namche	3,440m	Hike to ~3,900m, “climb high, sleep low” round one
Day 4	Tengboche	3,870m	Moderate gain, manageable after Namche acclimatisation
Day 5	Dingboche	4,410m	First night above 4,000m, some fatigue is expected
Day 6	Dingboche	4,410m	Hike to ~5,100m, “climb high, sleep low” round two
Day 7	Lobuche	4,940m	Approaching 5,000m, maximum hydration and rest
Day 8	Gorak Shep	5,160m	Highest overnight, early arrival and sleep by 8pm
Day 9	Pheriche (descent)	4,240m	Post-summit descent, altitude stress starts easing

When to Descend — The Rule That Saves Lives

The golden rule of altitude medicine is simple: if in doubt, descend. Never keep ascending with AMS symptoms. Never wait until morning if severe symptoms show up. Dropping just 300-500m reliably eases AMS symptoms within hours. We apply a strict no-ascent-with-AMS policy — nobody with active symptoms goes further up, regardless of group schedule, weather windows, or how badly someone wants to keep going. Your guide’s assessment is the final word here, not your own read on how you’re feeling.

Helicopter rescue and evacuation from anywhere on the route — Gorak Shep, Dingboche, Namche, anywhere in between — arrives within 2-4 hours in good weather. Your travel insurance covers the cost, but only when the policy explicitly includes trekking above 5,000m and helicopter evacuation. We confirm your insurance documentation before every departure precisely because a helicopter rescue without that coverage runs $4,000-7,000 out of pocket. Travel insurance isn’t optional on this trip — it’s a genuine booking requirement.

Frequently Asked Questions

Related Guides

• EBC Trek Package — full 12-day trip from $1,039 per person
• Altitude and Elevation Guide
• Day-by-Day Itinerary
• How Hard Is the EBC Trek?
• EBC Trek for Beginners
• EBC Trek Cost 2026

Know What to Watch For, Report It Early

Altitude sickness is the most serious risk on this route and also the most preventable. Learn the symptoms before you leave home. Follow the acclimatisation schedule without cutting a single corner. Drink 3-4 litres a day from Namche onward. Tell your guide about every headache the moment it happens — not in the morning, not after you’ve seen how you feel post-dinner. Early is always better than late. The altitude itself is manageable. The protocol works, when it’s actually followed.

We’ve guided EBC since 2018, based right here in Kathmandu — not a booking platform. When you message us, you’re talking to the team that manages altitude safety on this exact route every season. Ask us anything about AMS prevention, Diamox, the acclimatisation schedule, or what actually happens if symptoms show up, and you’ll get a real answer from people who’ve handled it on the trail — not a generic FAQ copy-pasted from somewhere else.

Package rates: $1,039 per person for 8-12 people, $1,089 for 5-7, $1,259 for 2-4, $1,379 solo. Lukla flights, all permits, and helicopter evacuation arrangement included.

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Questions about altitude sickness prevention, Diamox, or what to do if symptoms develop? Message us on WhatsApp — we typically reply within 12 hours.