Altitude sickness is the main health risk on the Everest Base Camp trek. Mild symptoms, like a headache and poor sleep, are common above 3,500m. Fitness does not protect you. What lowers the risk is a slow ascent, rest days, and going down if symptoms get worse.
This guide shows where on the route altitude sickness is most likely. It also explains how to recognise it and what to do. It is general planning information, not medical advice. Please see a doctor or travel clinic before you go.
What’s Inside This Guide
- Where on the trek it is most likely
- Symptoms of altitude sickness
- HACE and HAPE: the dangerous forms
- How to prevent altitude sickness
- Diamox and other medicines
- What happens if you get sick on the trek
- Frequently Asked Questions
- Related Planning Guides
Where on the Trek It Is Most Likely
Altitude sickness follows big gains in sleeping height. The Wilderness Medical Society advises adding no more than 500m of sleeping height a day above 3,000m. It also advises a rest day for every 1,000m gained. These are the nights on our 12-day itinerary to watch:
| Night | Where you sleep | Gain from the night before | Why it matters |
|---|---|---|---|
| 2 | Namche Bazaar, 3,440m | +830m | Biggest gain of the trek; rest day follows |
| 5 | Dingboche, 4,410m | +590m | First night above 4,000m; rest day follows |
| 7 | Lobuche, 4,940m | +530m | Cold, thin air, and the night before the hardest day |
| 8 | Gorak Shep, 5,164m | +224m | Highest night; poor sleep is normal here |
The rest days at Namche and Dingboche come straight after the two biggest gains. That is why we never cut either one. Our EBC elevation guide shows every night’s altitude in metres and feet.
Symptoms of Altitude Sickness
Acute mountain sickness, or AMS, usually starts within a few hours to a day of arriving somewhere higher. It often shows up during the first night. The main sign is a headache, with at least one other symptom:
- Loss of appetite, nausea or vomiting
- Tiredness or weakness beyond normal trekking fatigue
- Dizziness or light-headedness
- Poor sleep
| What you notice | What it probably means | What to do |
|---|---|---|
| Mild headache that eases with rest, water and a painkiller | Mild AMS, common above 3,500m | Tell your guide, rest, and don’t go higher until it clears |
| Headache plus nausea or no appetite, not improving | AMS | Stay at the same altitude for another night, or go down |
| Symptoms getting worse after a night’s rest | Worsening AMS | Go down |
| Confusion, stumbling, extreme drowsiness | Possible HACE | Go down now, whatever the time |
| Breathless at rest, wet cough, chest tightness | Possible HAPE | Go down now, with as little effort as possible |
Never hide symptoms from your guide to keep up with the group. Early AMS is easy to manage. Ignored AMS can turn dangerous.
HACE and HAPE: The Dangerous Forms
HACE, high altitude cerebral edema, is swelling of the brain. The person may seem drunk: confused, unsteady on their feet, or very sleepy. A simple test is to ask them to walk heel to toe in a straight line.
HAPE, high altitude pulmonary edema, is fluid in the lungs. Signs include breathlessness while resting, a persistent cough, chest tightness and, later, frothy or pink spit. It can develop without any AMS first.
Both are emergencies. The treatment is descent, usually by 300m to 1,000m or more, and medical care. Doctors also use oxygen and prescription medicines. Don’t wait until morning or for the weather to improve if you can safely go down.
How to Prevent Altitude Sickness
- Keep both rest days. Hike higher in the morning, then sleep lower. This is the most useful thing you can do.
- Walk slowly. You should be able to talk while walking uphill. If you can’t, slow down.
- Drink enough water. Aim for pale urine. Dehydration causes headaches that feel like AMS.
- Skip alcohol for the first days at a new altitude, and avoid sleeping pills that slow your breathing.
- Eat, even without appetite. Your body needs energy, and soups and rice are easy to get down.
- Speak up early. Tell your guide about any headache, however small.
If you have had altitude sickness before, tell us when you book. We can add a night at Dingboche or Lobuche.
Diamox and Other Medicines
Acetazolamide, sold as Diamox, helps your body acclimatise faster. It is prescription-only, so talk to your doctor before the trip. The Wilderness Medical Society’s guideline dose for prevention is 125mg every 12 hours for adults. It starts the day before you go higher. Your doctor will tell you how long to take it.
Common side effects include tingling in the fingers and toes, needing to pee more often, and fizzy drinks tasting flat. It is a sulfonamide, so tell your doctor if you are allergic to sulfa drugs. Try it at home first if your doctor agrees, so the side effects don’t surprise you on the trail.
Diamox does not replace the rest days. Trekkers taking it still get altitude sickness if they climb too fast. Ibuprofen has some evidence for prevention, but less than Diamox. Dexamethasone is a prescription medicine that doctors use mainly for treatment, not routine prevention.
What Happens if You Get Sick on the Trek
Your guide checks how you feel each day and makes the call on whether you go higher. If you have mild AMS, you usually rest another night at the same altitude. If symptoms get worse, you go down. On a solo trek, your guide goes down with you. In a group, a team member stays with you. Or you rest at a lodge while the group carries on, depending on the situation.
The Himalayan Rescue Association runs an aid post at Pheriche during the main trekking seasons, with volunteer doctors. In the spring climbing season, its Everest ER clinic operates at Base Camp. Helicopters can evacuate seriously ill trekkers when weather allows.
This is why your travel insurance must cover trekking to 5,644m and helicopter evacuation. A policy capped at 5,000m will not cover Kala Patthar or Gorak Shep. We ask for proof of insurance before we confirm your booking.
Frequently Asked Questions
Mild symptoms, like headaches and poor sleep, are common above 3,500m. Serious altitude sickness is much rarer, and a slow ascent with rest days lowers the risk.
It can start above about 2,500m, but on this route most symptoms appear from Namche Bazaar, at 3,440m, upwards. Dingboche, Lobuche and Gorak Shep are where it is most likely.
No. Fit people get altitude sickness too, and they sometimes climb too fast because they feel strong. Fitness makes the walking easier, not the altitude.
Ask your doctor. Many trekkers take it, and it does help, but it is prescription-only and has side effects. It never replaces the rest days in the itinerary.
Tell your guide, rest, drink water and take a painkiller if you normally can. Don’t go higher until it has gone. If it gets worse or comes with other symptoms, go down.
Yes, if someone ignores the signs of HACE or HAPE. Deaths are rare. They usually follow climbing too fast or carrying on with worsening symptoms. Going down early is the best protection.
Related Planning Guides
- Everest Base Camp Trek package — 12 days with two full rest days, from $1,039
- Everest Base Camp Trek Elevation — every altitude, and how fast the route climbs
- 12-Day EBC Itinerary — where you sleep each night
- How Hard Is the EBC Trek? — the hardest days and how to train
- Acclimatization in Nepal Trekking — how acclimatisation works on any trek
- EBC Packing List — what to bring for the cold
Two Rest Days, Never Cut
Our Everest Base Camp Trek costs $1,039 to $1,379 per person. It keeps both rest days on every departure. See the full trek details, or ask us on WhatsApp if you have had altitude sickness before.