Altitude Sickness: How to Prevent It and What to Do If It Happens
Acute mountain sickness affects approximately 25 percent of people who ascend rapidly to 8,000 feet and 75 percent of those who ascend rapidly above 14,000 feet. It is not primarily a fitness issue — ultra-fit individuals at sea level elevation can develop significant altitude sickness at the same rate as sedentary individuals. It is a physiological response to reduced oxygen partial pressure that occurs at altitude, and its management is straightforward once you understand the rules.
The Symptoms
Acute mountain sickness presents as headache combined with one or more of the following: fatigue, loss of appetite, nausea, dizziness, or difficulty sleeping. Headache alone at altitude is not diagnostic of AMS but warrants attention. The more serious conditions — high-altitude pulmonary edema (HAPE) and high-altitude cerebral edema (HACE) — can develop from unrecognized or untreated AMS and are life-threatening emergencies requiring immediate descent.
The Acclimatization Principle
The fundamental rule of altitude acclimatization: climb high, sleep low. Spend your highest-exertion time at higher elevations but return to lower elevations to sleep. The body acclimatizes primarily during sleep, and sleeping at lower elevations accelerates the process. Don’t ascend sleeping altitude by more than 1,000 feet per day above 8,000 feet. Build in a rest day at a middle elevation before ascending to high altitude. Staying well hydrated accelerates acclimatization; alcohol at altitude worsens symptoms significantly.
Treatment: Descent Is the Only Reliable Cure
Mild AMS that doesn’t worsen with rest and hydration over 24 hours may be managed in place. Any worsening of symptoms, any confusion or loss of coordination, or any difficulty breathing at rest requires immediate descent — not a wait-and-see approach. Acetazolamide (Diamox), available by prescription, prevents and treats AMS when taken prophylactically before ascent but does not substitute for appropriate acclimatization strategy.
