Altitude sickness (Acute Mountain Sickness, or AMS) is the single most common reason trekkers turn back before reaching Everest Base Camp. It is also largely preventable with the right itinerary, the right protocol, and the right attitude toward the one thing altitude trekking requires above all else: patience.
This guide covers how altitude sickness works, what the symptoms are at different stages of severity, the acclimatization strategy that works, Diamox, and the critical rule about when to descend rather than push on.
As altitude increases, air pressure falls and the same volume of air contains fewer oxygen molecules. Above 2,500m, most people's bodies begin to respond to this reduced oxygen with a cascade of physiological adjustments: increased breathing rate, increased heart rate, and - over several days - increased red blood cell production. The problem arises when the ascent is faster than the body's adjustment capacity.
Altitude sickness is not a sign of weakness and is not prevented by fitness. A highly trained athlete who ascends too quickly will develop AMS. A moderately fit person who follows correct acclimatization protocol will often reach Base Camp without significant symptoms.
| Level | Symptoms | Action |
|---|---|---|
| Mild AMS | Headache, fatigue, dizziness, poor sleep, reduced appetite | Rest, hydrate, do not ascend further until symptoms resolve |
| Moderate AMS | Severe headache unresponsive to painkillers, nausea/vomiting, extreme fatigue, difficulty walking straight | Descend immediately by at least 500m |
| Severe: HAPE/HACE | Crackling in lungs, pink/frothy cough (HAPE); confusion, loss of coordination, inability to walk (HACE) | Emergency descent and evacuation NOW - life-threatening |
HAPE (High Altitude Pulmonary Edema - fluid in the lungs) and HACE (High Altitude Cerebral Edema - fluid on the brain) are medical emergencies. Helicopter evacuation from the Khumbu costs USD 5,000-15,000 - which is why adequate travel insurance with helicopter rescue coverage is non-negotiable. See our EBC cost guide for insurance recommendations.
All responsible EBC itineraries include two acclimatization days: one at Namche Bazaar (3,440m) and one at Dingboche (4,410m).
Namche acclimatization day: Hike to the Everest View Hotel (3,880m) or Khumjung village (3,790m). Return to sleep at 3,440m. This "climb high, sleep low" principle forces the body to produce more red blood cells at the day's peak altitude while allowing the best possible sleep at the lower overnight elevation.
Dingboche acclimatization day: Hike toward Nangkartshang Peak to approximately 5,090m. Return to sleep at 4,410m. This is the single most important acclimatization day on the entire trek - it prepares the body for the 4,940m-5,545m section still to come.
Do not skip these days. Trekkers who skip acclimatization days to save time consistently have higher rates of AMS and higher rates of incomplete treks.
Never ascend with symptoms. If you have a headache or nausea at the current elevation, do not move up. Rest for 24 hours. If symptoms improve, you may continue. If symptoms worsen, descend.
Hydrate constantly. Aim for 3-4 litres of water per day throughout the trek. Pale-to-clear urine is your best hydration indicator. Dehydration worsens altitude sickness significantly.
Walk slowly. Your guide will set a pace - follow it, even if it feels too slow at lower elevations. The "rest step" (a brief pause at each step above 4,500m) is a real technique used by mountaineers for a reason.
Avoid alcohol above 3,500m. Alcohol dehydrates and suppresses respiratory drive - both dangerous at altitude.
Descend if in doubt. The descent cure is the most reliable altitude sickness treatment available. Even descending 300-500m produces measurable improvement in most AMS cases.
Diamox is a medication that accelerates the body's acclimatization process by stimulating the kidneys to excrete bicarbonate, which in turn increases breathing rate and improves oxygen uptake. It genuinely works. Side effects include increased urination (significant at altitude), tingling in fingers and toes, and altered taste of carbonated drinks. Some people are allergic.
The mainstream medical guidance: Diamox is appropriate for trekkers with a history of altitude sickness, those on aggressive itineraries with limited acclimatization time, and those above 3,000m who develop significant AMS symptoms. It is not a substitute for correct acclimatization protocol. Discuss Diamox with your own doctor before departure - the standard prophylactic dose is 125-250mg twice daily, starting 24 hours before significant altitude gain.
A pulse oximeter measures blood oxygen saturation (SpO2) and heart rate. Normal SpO2 at sea level is 96-100%. Expected reductions at altitude: 88-92% at Namche (3,440m), 82-88% at Dingboche (4,410m), 75-85% at Gorak Shep (5,140m). Readings below 75% at any altitude, or readings dropping faster than expected, warrant medical attention. Our guides carry pulse oximeters and take regular readings from Day 3 onward.
Turning back from an EBC trek because of AMS is not failure. It is the correct decision when your body tells you it has reached its limit for that journey. The mountains are permanent; the window for another attempt can be planned. Pushing through moderate AMS symptoms to HACE or HAPE territory risks not returning at all.
If your guide recommends descent, do not argue. Licensed EBC guides are trained in altitude sickness recognition specifically, and their recommendation to descend is based on observing your symptoms against their experience of hundreds of trekkers at the same elevation. Trust it.
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Getaway Nepal Adventure (P.) Ltd.
Thamel Kathmandu, Nepal
Tel: +977 98510 38 908
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