Check a high-altitude itinerary and recognize warning signs
Sleeping altitude matters more than the highest point reached during the day. Review ascent pace, when to stop climbing, and signs that need urgent descent.
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Plan by sleeping altitude, not the day’s highest point
Acclimatization varies between people, and no itinerary guarantees prevention. The CDC Yellow Book and Wilderness Medical Society emphasize changes in sleeping altitude over daytime peaks. CDC advises avoiding a direct ascent in one day from low altitude below 1,200 m to a sleeping altitude of 2,750 m or higher, then limiting sleeping-altitude gains to 500 m per day above 3,000 m and adding an acclimatization day for each 1,000 m gained. These are planning references, not a safety guarantee for every traveler. CDC Yellow Book · Wilderness Medical Society 2024 guideline
Stop ascending when symptoms appear
After a recent ascent, headache with nausea, fatigue, loss of appetite, or dizziness can be consistent with acute mountain sickness, but other causes such as dehydration, infection, or medicines may also explain symptoms. With mild symptoms, do not climb higher and monitor how they change. If symptoms fail to improve with rest, seek local medical help. If symptoms worsen at the same altitude despite treatment, descent is mandatory. Request rescue or medical support and do not ascend while waiting for help. CDC describes descent as an effective response, but no single descent distance guarantees the right response for every situation.
Changes in thinking, walking, or breathing are urgent
Confusion, reduced alertness, or inability to walk steadily can signal high-altitude cerebral edema. Breathlessness at rest or worsening cough can indicate a serious condition such as high-altitude pulmonary edema. Stop ascending and seek emergency rescue or medical help and descent. If oxygen is available, use it under the direction of medical or rescue personnel. Small handheld oxygen cans do not provide sustained treatment. CDC treatment guidance
Follow individual advice about medicines and fluids
A clinician may consider acetazolamide for prevention or acclimatization in some itineraries, but it is not a substitute for a gradual ascent. Tell the prescriber about a severe reaction to sulfonamide medicines or a history of Stevens–Johnson syndrome. Do not decide whether to take the medicine from this article. Thirst or dehydration should not be described as a cause of altitude illness. Discuss the itinerary, prior altitude illness, conditions, and medicines with a travel- or wilderness-medicine professional before departure.