Altitude sickness is the single biggest reason trekkers fail to reach their goal. In over two decades of guiding in the Himalayas, Andes, and African peaks, I have seen altitude sickness cut short hundreds of journeys that were well within reach. The good news: almost all cases are entirely preventable with the right knowledge and approach.
What Is Altitude Sickness?
Altitude sickness, or Acute Mountain Sickness (AMS), occurs when your body does not acclimatize quickly enough to reduced oxygen levels at elevation. Above 2,500 metres, the air contains less oxygen per breath. Your body compensates by breathing faster and increasing red blood cell production — but this takes time. If you ascend faster than your body adapts, symptoms develop.
AMS affects people of all fitness levels. Elite athletes are not immune. In fact, being highly fit can work against you if it encourages you to ascend too quickly.
Important: Altitude sickness symptoms must always be taken seriously. What begins as mild AMS can progress to High Altitude Cerebral Edema (HACE) or High Altitude Pulmonary Edema (HAPE) — both life-threatening conditions requiring immediate descent.
Recognising the Symptoms
Early symptoms of AMS typically appear 6 to 12 hours after arrival at high altitude and include:
- Headache — the most common and reliable early warning sign
- Fatigue and weakness beyond normal trekking tiredness
- Loss of appetite and nausea
- Dizziness or lightheadedness
- Difficulty sleeping despite exhaustion
- Shortness of breath at rest (not just during exertion)
If symptoms worsen, become severe, or are accompanied by loss of coordination, confusion, or a persistent cough producing pink frothy sputum, descend immediately and seek medical attention.
The Golden Rules of Altitude Acclimatization
Rule 1: Ascend Slowly
The universal guideline above 3,000 metres is to increase your sleeping altitude by no more than 300 to 500 metres per day. This is the single most effective prevention measure. Our Everest Base Camp itinerary, for example, includes two specific acclimatization days — at Namche Bazaar and Dingboche — built specifically around this principle.
Rule 2: Climb High, Sleep Low
This classic mountaineering principle means you can hike to a higher elevation during the day and then return to a lower camp to sleep. Day hikes to higher elevations stimulate red blood cell production while sleeping at lower altitude allows your body to consolidate the gains. We use this on multiple days of our Kilimanjaro Lemosho Route with the Lava Tower acclimatization hike.
Rule 3: Hydrate Aggressively
Dehydration worsens altitude sickness symptoms significantly. At altitude, you lose moisture faster through respiration and the dry mountain air. Aim for at least 3 to 4 litres of water per day. Avoid alcohol in the first few days at altitude — it disrupts sleep quality and accelerates dehydration.
Guide's Tip: The Headache Test
Every morning I ask my group to rate their headache on a scale of 0 to 10. A score of 3 or higher means we slow down or take a rest day. No ego, no pressure. The mountain will always be there. This simple daily check has prevented dozens of serious AMS cases in my career.
Rule 4: Never Ascend With Symptoms
If you have any AMS symptoms — especially a headache — do not go higher. Rest at your current altitude. In most cases, mild AMS resolves within 24 to 48 hours if you stop ascending. If symptoms do not improve or worsen, descend immediately. Even 300 to 500 metres of descent can bring dramatic relief.
Rule 5: Know When to Descend
No summit, no matter how much you have dreamed of it, is worth your life. The mountain will still be there. A forced descent is not a failure — it is excellent decision-making. Every experienced guide knows that the ability to turn around is the mark of a true mountaineer.
Does Medication Help?
Acetazolamide (Diamox) is a prescription medication commonly used to prevent and treat AMS. It works by stimulating faster breathing, helping your body process oxygen more efficiently. It is effective but comes with side effects including increased urination, tingling in hands and feet, and in rare cases allergic reactions (it is a sulfa drug — avoid if you are allergic to sulfa antibiotics).
We always recommend consulting your doctor before your trek to discuss whether Diamox is appropriate for you. It is a supplement to proper acclimatization — not a replacement for it.
Pre-Trek Preparation
While no preparation guarantees AMS immunity, being well-prepared helps:
- Build cardiovascular fitness with regular aerobic exercise in the months before your trek
- Sleep at moderate altitude (1,500 to 2,000m) if possible in the nights before beginning your high-altitude ascent
- Arrive in good health — cold and flu symptoms are significantly worsened by altitude
- Avoid flying directly to very high starting points where possible
The Bottom Line
Altitude sickness is predictable, manageable, and in most cases preventable. Choose an itinerary with proper acclimatization built in, listen to your body, stay hydrated, and trust your guide. With the right approach, the world's greatest high-altitude treks are within reach of any determined, well-prepared trekker.
On all Trekkership high-altitude treks, our guides carry pulse oximeters and perform daily health checks on every client. Your safety is always our first priority — and that means we never push the pace for the sake of the itinerary.
Marcus Trail
A certified mountain guide with Trekkership since 2011. Expert in high-altitude trekking, wilderness safety, and cultural immersion travel. All articles are based on first-hand experience guiding thousands of trekkers across the world's greatest trails.
