High-Altitude Sickness: Symptoms, Remedies, & How to Prevent It

Even experienced hikers can underestimate the effect ascents might have on their bodies or how long it takes to adjust to altitude. High-altitude sickness can develop within hours, with symptoms ranging from a dull headache to severe disorientation. This article explains what altitude sickness is and how to recognize the symptoms and stages of altitude sickness while hiking. It also covers potential methods for how to prevent altitude sickness or mitigate its effects and offers advice on when to descend.

What is considered high altitude and what does altitude sickness feel like?

The Wilderness Medical Society defines high altitude as 8,000+ feet. Starting around 8,200 feet, oxygen levels are low enough to trigger mountain sickness symptoms in unacclimatized hikers who haven’t trained for high-altitude hiking. Altitude sickness is essentially the body's response to a drop in oxygen levels and can include a throbbing headache, nausea, loss of appetite, dizziness, and poor sleep, similar to a hangover. Symptoms typically arise 6-12 hours after reaching high altitude and peak after the first night.

What are the three stages of altitude sickness?

High-altitude sickness generally follows three stages, each with its own associated mountain sickness symptoms. Recognizing these symptoms are a basic part of hiking first aid.

Mild symptoms: acute mountain sickness (AMS)

This accounts for most high-altitude sickness cases and shows up as a headache paired with nausea, fatigue, dizziness, and/or trouble sleeping. Acute mountain sickness symptoms usually develop at 8,200-11,500 feet.

High-altitude pulmonary edema (HAPE)

This buildup of fluid in the lungs typically appears after 1-4 days spent above 8,200 feet. Symptoms include breathlessness at rest, a potentially productive cough with pink sputum, chest tightness, and blue-tinged lips.

High-altitude cerebral edema (HACE)

This most dangerous stage of high-altitude sickness involves brain swelling. Symptoms include confusion, a severe headache that doesn’t respond to pain relievers, drowsiness, and ataxia (decreased muscle control). Left untreated, HACE can progress to a comatose state within 24 hours.

Common questions about high-altitude sickness

What’s the fastest way to get rid of altitude sickness?

Stop ascending, rest, hydrate, and take painkillers for your headache. Make sure you have extra water and meds on hand in your hiking pack or in a flask. Descending 1,000+ feet provides the fastest relief.

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How long does altitude sickness last?

Mild AMS usually resolves within 24-48 hours if you stop ascending and rest. HAPE and HACE improve within hours of descent.

Are there foods that help with altitude sickness?

While your hiking food plan may not prevent altitude sickness on its own, carbohydrate-rich foods such as pasta, rice, and fruit are the traditional go-tos at altitude, and several studies suggest a high-carb diet may ease AMS symptoms. Sports-nutrition guidance recommends getting 60% or more of your calories from carbs while hiking.

Can altitude sickness happen after you return home?

It’s uncommon to experience altitude sickness after returning home, though mild symptoms can linger for a day or two. A rarer condition, re-entry HAPE, affects people living at high altitude, usually within 24 hours of returning home.

High-altitude sickness: know the signs

Training for high-altitude running or hiking can be effective prevention, but knowing the signs of altitude sickness and its stages is vital, whether you’re tackling your first 10,000-foot mountain or thru-hiking the Pacific Crest Trail. Assess your high-altitude sickness symptoms to determine if you’re experiencing AMS, HAPE, or HACE and decide whether to stop and rest, medicate, or descend immediately. While it is possible to mitigate the effects of high-altitude sickness or slow its progression, descending is the surest way to promote recovery.