Altitude Sickness
Altitude sickness is a group of symptoms caused by reduced oxygen at high elevations, typically above 2,500m.
Altitude sickness is a group of symptoms caused by reduced oxygen at high elevations, typically above 2,500m.
Also known as
Acute mountain sickness, AMS, Soroche, High altitude illness, HACE, HAPE
Why travellers need to know
Altitude sickness is entirely predictable and largely preventable, yet it catches thousands of travellers every year because they underestimate how quickly symptoms develop. It affects fit and unfit people equally. The only reliable prevention is gradual ascent. Popular destinations at altitude include Cusco (3,400m), La Paz (3,640m), Lhasa (3,650m), and Kilimanjaro summit (5,895m). Pre-existing heart or lung conditions increase risk significantly.
Real-world example
You fly directly from sea level to Cusco, Peru (3,400m). Within 6 hours you have a splitting headache, nausea, and can barely walk up a flight of stairs. Your hotel gives you coca tea and advises rest. After 36 hours of acclimatisation, the symptoms ease. If you'd flown to Lima first and taken the bus up gradually, the adjustment would have been far less severe.
Country-specific notes
🇵🇪 Peru
Cusco sits at 3,400m; most visitors feel symptoms
Most travellers flying directly to Cusco from sea level experience some altitude symptoms. Hotels and restaurants routinely offer coca tea (mate de coca). Pharmacies sell acetazolamide (Diamox) over the counter. The Sacred Valley (2,800m) is a lower-altitude alternative for the first night.
Spend your first night in the Sacred Valley (Ollantaytambo or Urubamba) at 2,800m before moving up to Cusco. This single step reduces symptoms significantly.
🇳🇵 Nepal
Trekking routes routinely exceed 4,000m
Everest Base Camp (5,364m) and Annapurna Circuit routes take trekkers well above altitude sickness thresholds. Nepali trekking culture has well-established acclimatisation protocols. Most guided treks build in rest days, but independent trekkers must manage their own ascent rate.
Follow the rule of ascending no more than 300-500m per day above 3,000m with a rest day every 3rd day. Descend immediately if symptoms worsen.
🇹🇿 Tanzania
Kilimanjaro (5,895m) has a summit failure rate of 30–50% largely due to altitude sickness on short routes
Most Kilimanjaro routes don't allow sufficient acclimatisation time. Lemosho and Northern Circuit routes (7–9 days) have lower altitude sickness rates than the Marangu route (5 days). Acetazolamide (Diamox) is widely used as prophylaxis.
Consult a travel clinic about acetazolamide before Kilimanjaro — starting 2 days before ascent and continuing through descent significantly reduces acute mountain sickness risk.
Frequently asked questions
Does fitness level protect against altitude sickness?
No. Altitude sickness affects fit and unfit people equally. Physical fitness does not speed up acclimatisation. The only reliable prevention is gradual ascent. Some people are genetically more susceptible regardless of fitness.
Should I take Diamox (acetazolamide) preventively?
Diamox can help with acclimatisation but is not a substitute for gradual ascent. It's commonly taken starting 1-2 days before reaching altitude. It requires a prescription in most countries (though available OTC in Peru and Nepal). Discuss with your doctor, especially if you have sulfa allergies.
Your Nomedic record flags any heart or lung conditions that increase altitude risk, so a trekking doctor can assess you accurately at altitude.