Altitude sickness is the most common medical concern on Nepal treks, and the most preventable. It affects trekkers of all fitness levels — athletic ability does not protect you. The only reliable prevention is ascending slowly and allowing your body time to acclimatise. This guide explains the different forms of altitude sickness, how to recognise them, and what to do if symptoms develop.
What Is Altitude Sickness?
Altitude sickness occurs when you ascend faster than your body can adjust to lower atmospheric oxygen levels. It typically begins above 2,500m, though some individuals feel symptoms as low as 2,000m. There are three forms, ranging from uncomfortable to life-threatening:
1. Acute Mountain Sickness (AMS) — Mild to Moderate
AMS is the most common form. Symptoms usually appear 6–12 hours after reaching altitude and may worsen overnight.
- Headache (the defining symptom — especially throbbing and worsened by exertion)
- Fatigue and weakness
- Loss of appetite, nausea
- Dizziness
- Difficulty sleeping
Action: Stop ascending. Rest at the same altitude for 24–48 hours. Drink fluids. Take ibuprofen or paracetamol for headache. Do not go higher until symptoms have completely resolved.
2. High Altitude Cerebral Oedema (HACE) — Severe, Life-Threatening
HACE is AMS that has progressed to swelling of the brain. It is a medical emergency.
- Severe, worsening headache that does not respond to pain medication
- Confusion, disorientation, irrational behaviour
- Loss of coordination (ataxia) — check by walking heel-to-toe in a straight line
- Drowsiness progressing to unconsciousness
Action: Descend immediately, even in darkness. Do not wait for morning. Descend at least 300–500m or until symptoms improve. Call for helicopter evacuation.
3. High Altitude Pulmonary Oedema (HAPE) — Severe, Life-Threatening
HAPE is fluid accumulation in the lungs. It can develop rapidly and is the most common cause of altitude-related death among trekkers.
- Shortness of breath at rest (not just during exertion)
- Persistent dry cough, often producing pink or frothy sputum
- Extreme fatigue
- Lips or fingertips turning blue (cyanosis)
Action: Descend immediately. This is a life-threatening emergency. Do not sleep on it. Call for helicopter evacuation.
The Golden Rule: Do Not Ascend With Symptoms
Any combination of headache plus at least one other AMS symptom means do not go higher until you have fully recovered. Pushing on is the leading cause of AMS progressing to HACE or HAPE. Eco Holiday Asia guides are trained to enforce this rule regardless of group pressure.
Prevention: Acclimatisation Schedule
The most effective prevention is a properly paced ascent. The standard guideline above 3,000m is: ascend no more than 300–500m of sleeping altitude per day, with a rest day every 3rd day.
Built-in Acclimatisation Days on Key Eco Holiday Asia Treks
| Trek | Key Acclimatisation Stops |
|---|---|
| Everest Base Camp (14+ days) | Namche Bazaar (3,440m, 2 nights), Dingboche (4,410m, 2 nights) |
| Annapurna Circuit (14+ days) | Manang (3,519m, 2 nights before Thorong La) |
| Manaslu Circuit (14+ days) | Samagaon (3,530m, 2 nights before Larkya La) |
| Upper Mustang (12+ days) | Jomsom (2,743m overnight) before ascending to Lo Manthang |
Diamox (Acetazolamide): What You Should Know
Diamox is a prescription drug that helps speed acclimatisation by stimulating breathing. However:
- Consult your doctor before taking Diamox. It is contraindicated for people with sulfa allergies.
- Common side effects include increased urination, tingling in hands and feet, and altered taste of carbonated drinks.
- Diamox is not a substitute for proper acclimatisation. Do not use it to ascend faster than your body is ready for.
Hydration and Nutrition at Altitude
- Drink 3–4 litres of water per day at altitude, more if you are sweating heavily
- Avoid alcohol for the first 48 hours after arriving at high altitude
- Eat high-carbohydrate meals (dal bhat, noodles, rice) — carbs require less oxygen to metabolise than fats or proteins
- Avoid sedatives and sleeping tablets, which suppress breathing and can worsen hypoxia
Emergency Helicopter Evacuation
Helicopter rescue from above 3,000m can cost USD 3,000–10,000+ depending on altitude and distance. Travel insurance covering emergency helicopter evacuation is mandatory for all Eco Holiday Asia trekking clients. Ensure your policy explicitly covers Himalayan trekking altitudes and helicopter rescue.
Quick Symptom Reference
| Symptom | AMS | HACE | HAPE |
|---|---|---|---|
| Headache | Yes | Severe | Sometimes |
| Confusion / ataxia | No | Yes | No |
| Breathless at rest | No | Sometimes | Yes |
| Cough (productive) | No | No | Yes |
| Action required | Stop ascending; rest | Descend now | Descend now |
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