Understand altitude sickness and learn how to acclimatize safely for Himalayan trekking. Medical guidance from trekking experts.
Altitude sickness (Acute Mountain Sickness or AMS) occurs when your body is exposed to lower oxygen levels at high elevations. The higher you go, the less oxygen is available, and your body needs time to adapt.
At sea level, the air contains about 21% oxygen. At 2,500 meters (8,200 ft), the oxygen available drops to about 60% of what you're used to at sea level. Your lungs must work harder to absorb oxygen, your heart rate increases, and your body experiences various physiological changes.
Most people can reach 2,500m without major problems. Between 2,500m and 3,500m, mild symptoms are common. Above 3,500m, altitude effects become more pronounced. Nepal's trekking routes climb well above this level, so understanding acclimatization is critical.
Altitude sickness can affect anyone, regardless of age, fitness level, or health. Even elite athletes can experience it. Prior altitude experience helps but doesn't guarantee immunity. Younger people sometimes experience worse symptoms because they ascend too quickly.
Headache, fatigue, nausea, dizziness, difficulty sleeping. Usually appears within 6-12 hours of arrival at altitude.
Severe headache, confusion, coordination loss, ataxia (loss of balance). Requires immediate descent to lower elevation.
Shortness of breath at rest, fluid in lungs, loss of consciousness. Medical emergency — requires immediate descent and evacuation.
Most common symptom. Usually mild to moderate. Responds to rest and hydration.
Often accompanies headache. Usually subsides with rest and acclimatization.
Your body works harder at altitude. Sleep may be disrupted and dreams vivid.
Even light activity feels more strenuous. This is normal and typically improves.
Feeling lightheaded or disoriented. Rest and acclimatization usually help.
Waking frequently or unusual sleep patterns. Acclimatization improves this.
The best strategy is to ascend slowly, spend rest days at intermediate altitudes, and listen to your body. "Climb high, sleep low" is the gold standard.
Arrive and rest. Spend first night at moderate altitude to begin acclimatization.
Gradual ascent with one rest day. Namche is the main acclimatization hub for EBC treks.
Critical acclimatization day. Light activity like hiking to local viewpoints. Sleep low strategy continues.
Day hike to higher altitude, return to Namche to sleep. Then trek higher to Tengboche (3,867m).
Another rest day to allow further acclimatization before continuing higher.
Climb higher with gradual daily ascent. More rest days scheduled as altitude increases.
Pro tip: A typical 12-14 day Everest Base Camp trek includes 4-5 rest or acclimatization days. Faster treks (9-10 days) increase altitude sickness risk. Our guides always recommend slower pacing.
Drink 3-4 liters of water per day. Dehydration worsens altitude symptoms. Electrolyte drinks help.
Never gain more than 500m per day above 2,500m. Rest days at intermediate altitudes are critical.
Rest days mean easy hiking to higher altitude, then sleeping lower. Avoid strenuous exercise.
Diamox (acetazolamide) prescribed by doctors helps acclimatization. Consult your doctor before trekking.
Eat high-calorie foods and carbohydrates. Your body burns 2-3x more calories at altitude.
Sleeping slightly elevated (extra pillow) can ease breathing. Altitude tents available for serious climbers.
Our guides are trained in altitude management and safety. We build acclimatization into every trek itinerary. Ask us about altitude medicine and preparation.