How to Prevent Altitude Sickness (AMS) on Your Himalayan Trek
Altitude sickness can ruin your trek. Learn the early symptoms of AMS and the proven acclimatization rules to keep yourself safe.
Acute Mountain Sickness (AMS) does not care about your age, your gender, or how many marathons you have run at sea level. Anyone trekking above 3,000 meters in Nepal is at risk.
The air at Everest Base Camp contains about 50% less oxygen than at sea level. While this sounds intimidating, altitude sickness is entirely preventable if you follow the golden rules of acclimatization. Here is how to protect yourself and ensure you reach your goal safely.
1. Understanding the Symptoms
The most dangerous thing you can do in the Himalayas is hide your symptoms from your guide. Your guide is trained in Wilderness First Aid to help you, but they can only do so if you are honest about how you feel.
Early Warning Signs of AMS
- Throbbing Headache
- Loss of Appetite / Nausea
- Extreme Fatigue / Insomnia
- Dizziness or Lightheadedness
*If you experience a severe headache that does not go away with painkillers, extreme shortness of breath while resting, or loss of coordination, these are signs of severe AMS (HACE or HAPE). You must descend immediately.
2. The Golden Rules of Acclimatization
Your body needs time to create more red blood cells to carry the limited oxygen. You cannot rush this process. Follow these three unbreakable rules:
Climb High, Sleep Low
This is the mantra of mountaineering. During your acclimatization days (like in Namche Bazaar), you will hike up to a higher elevation during the day (e.g., the Everest View Hotel at 3,880m), but you will return to sleep at a lower altitude (Namche at 3,440m). This stresses the body safely and allows it to recover overnight.
The 500-Meter Rule
Once you pass the 3,000-meter mark (roughly around Namche Bazaar), you must never increase your sleeping elevation by more than 500 meters (1,640 feet) in a single day. Even if you arrive at your tea house at 1:00 PM and feel perfectly fine, do not push higher.
Mandatory Rest Days
For every 1,000 meters you gain above 3,000m, you must take a full rest day. On the standard EBC trek, this means spending two nights in Namche Bazaar (3,440m) and two nights in Dingboche (4,410m). Do not skip these days to save time.
3. Hydration and Medication
Aggressive Hydration
At high altitudes, you lose moisture rapidly just by breathing the dry, cold air. Dehydration perfectly mimics AMS symptoms (headache, fatigue). You must drink a minimum of 3 to 4 liters of water a day. Tip: Bring flavor drops or electrolytes, as plain water gets hard to drink in those quantities!
Diamox (Acetazolamide)
Many trekkers use Diamox to prevent AMS. It works by acidifying your blood, which tricks your body into breathing deeper and faster, especially while sleeping. It is highly effective but has side effects (tingling fingers, frequent urination). Always consult a travel doctor before your trip to get a prescription.
"Local remedies like Garlic Soup are delicious and warming, but they are not a cure for altitude sickness. The only true cure for AMS is descending to a lower altitude."