Gradually increase your sleeping altitude when heading to high elevations; if symptoms worsen, descend immediately — don’t tough it out.

33. Gradually increase your sleeping altitude when heading to high elevations; if symptoms worsen, descend immediately — don’t tough it out.

Cost: It requires an extra day or two for acclimatization. Preventive medications are prescription-only, so you must consult a doctor before traveling. The main challenge is fitting these days into an otherwise tight itinerary.

In plain terms: This guideline focuses on sleeping altitude, not daytime elevation. Sleeping above 2,450 meters already poses a risk of altitude sickness. Once above 3,000 meters, you should only raise your nighttime altitude by 500 meters per night, allowing an additional day of acclimatization for every 1,000-meter increase. Symptoms such as headache, nausea, unsteady gait, altered mental state, or shortness of breath even at rest indicate the need to descend. Descending takes priority over oxygen therapy or medication.

Benefit: Sleeping above 2,450 meters increases the risk of altitude sickness. Without prompt descent, high-altitude cerebral edema and pulmonary edema — fluid buildup in the brain and lungs — can be fatal.

Evidence grade: A

Sources: U.S. Centers for Disease Control and Prevention. Yellow Book High Altitude Travel and Altitude Sickness: "Any unacclimatized traveler proceeding to a sleeping altitude of ≥2,450 m (≥8,000 ft)—and sometimes lower—is at risk for altitude illness"; Ascent rate "500 m (1,650 ft) per night in sleeping altitude once above 3,000 m (9,800 ft)" 1000 meters plus acclimatization day; Acetazolamide prophylaxis "125 mg twice a day; 250 mg twice a day if >100 kg body weight"; "If symptoms become worse despite rest or treatment at the same elevation" must be withdrawn. <https://www.cdc.gov/yellow-book/hcp/environmental-hazards-risks/high-altitude-travel-and-altitude-illness.html>; Wilderness & Environmental Medicine (2024). Clinical Practice Guidelines for the Prevention, Diagnosis, and Treatment of Acute Mountain Sickness (2024 Update). Wilderness & Environmental Medicine. <https://doi.org/10.1016/j.wem.2023.05.013>

Notes: The rule specifically refers to sleeping altitude, not daytime elevation. Headache, nausea, unsteadiness, confusion, or breathlessness at rest are clear signs to descend. Descending should always come before oxygen use or medication; continuing upward while on oxygen is unsafe.