Altitude Sickness: How to Prevent It and Treat It

Fitness will not save you from altitude sickness, and neither will drinking water. The single thing that causes acute mountain sickness is gaining altitude too fast without acclimatization, and the most reliable way to prevent it is to climb slowly enough that your body can adjust. This matters for any flatlander or coastal dweller heading into the mountains with an elk or sheep tag, because the mountains do not care how many miles you run or how clean your lungs are.

That is the hard part to accept. A professional baseball player in peak condition can have his hunt cut short by symptoms that appear on day two, while a Miami cigar smoker who never puts one down feels fine the whole trip. Cody Arnold, who guided hunters near Granby, Colorado, for two decades, watched both happen. Susceptibility is in part genetically determined, and there is no simple test to predict who will suffer. Below is how to stack the odds in your favor and what to do when prevention fails.

What Is Actually Happening to You

Altitude sickness is a mild form of hypoxia, meaning the tissues of your body do not receive enough oxygen. As you climb, the air holds less oxygen, and your systems need time to catch up. At around 10,000 feet the inspired oxygen pressure is only 69 percent of what it is at sea level (enough to leave your blood measurably short of oxygen on quick exposure). How hard that hits you depends on the altitude, how fast you ascended, and how long you stay.

Pre-existing cardiovascular and respiratory conditions complicate the adjustment, and travelers with compromised lung function must be cautious because increased breathing is central to adapting. Curiously, people with asthma often feel better at altitude than at sea level, since the mountain air lacks the allergens and humidity that aggravate their symptoms. Alcohol, dehydration, and poor fitness are frequently blamed but do not trigger or worsen the illness. A hangover feels similar and will make you miserable, but it is not altitude sickness.

The Symptoms, from Mild to Dangerous

Recognizing where you fall on the scale keeps you and your group safe. Mild symptoms may surface a day or so after you fly into a high airport or while you hike into camp, and they should ease after a few days of acclimatizing. Watch for dizziness, fatigue, shortness of breath, loss of appetite, a minor headache, mild nausea, and trouble sleeping.

If you keep climbing without letting your body catch up, symptoms worsen. Chest tightness, dizziness or fatigue that stops you from walking, moderate to severe headache and nausea, and vomiting mark the moderate stage. At that point the standard recommendation is to descend to a lower altitude.

Severe symptoms are a medical emergency. Shortness of breath at complete rest, confusion paired with denial of symptoms, and the inability to stand unassisted all demand immediate descent. The two conditions to fear are high-altitude pulmonary edema, or HAPE, where fluid pools in the lungs and produces a feeling of suffocation, and high-altitude cerebral edema, or HACE, where fluid gathers in the brain and causes lack of coordination, aggression, and confusion. Either one warrants medical attention as fast as you can get it.

Your Real Risk Before You Go

Training and physical fitness do not affect your risk. Sex plays a minimal role. Children are as susceptible as adults, and people over 50 carry slightly less risk. Anyone unacclimatized who proceeds to a sleeping altitude of 8,000 feet or more is at risk, and sometimes lower elevations produce trouble. Even after you adjust to one altitude, moving to a higher sleeping altitude puts you at risk again, especially when the gain runs 2,000 to 3,000 feet.

The most reliable guide is how you responded on a previous trip, but only when the altitude and rate of ascent are similar, and even then it is not an infallible predictor. The CDC ranks risk by three factors: your history of altitude illness, your sleeping altitude on the first day, and your ascent rate. A first-night sleeping altitude under 9,000 feet with a modest history sits in the low-risk category. Sleeping above 11,150 feet on day one, or a prior bout of HAPE or HACE, pushes you into high risk.

Ascend Slowly and Sleep Low

Your body can adjust to moderate hypoxia at altitudes up to roughly 17,000 feet, but the acute acclimatization process takes time. It unfolds over the first three to five days after you arrive, bringing a steady increase in ventilation, better oxygenation, and changes in cerebral blood flow. Altitude illness can develop before that process finishes, but not afterward. That window is the entire game.

The goal is to avoid going too high too fast. Spending a minimum of two to three nights at around 8,000 to 9,000 feet before climbing higher is strongly protective against acute mountain sickness. The Wilderness Medical Society says you should avoid ascending to a sleeping altitude of 9,000 feet or more in a single day. Once above about 9,800 feet, the same guidance holds your gain in sleeping altitude to no more than 1,650 feet per night, and adds an extra acclimatization night for every 3,300 feet of sleeping altitude you gain.

Sleeping altitude matters more than your daytime high point, because hypoxemia is worst during sleep. A day trip to a high destination with a return to lower ground each evening is far less stressful on the body. Climb high, sleep low is the working rule. These recommendations still run too fast for some travelers and too slow for others, so treat them as a starting point rather than a guarantee.

Fitness Helps, but It Is Not Armor

Being in shape will not prevent altitude sickness, but it does help you perform under exertion with less available oxygen. The difficulty is that the effect is hard to replicate without actually traveling to the elevation where you will hunt. One option is to add an altitude mask to your standard cardio workouts. You may feel like Bane from Batman at first, but over time you may notice your cardiovascular system tolerating lower oxygen better. Keep the expectation honest: fitness earns you a stronger engine, not immunity.

When It Strikes, Get Down

If mild symptoms appear, stop gaining altitude and give your body time to adjust before you climb any higher. If symptoms reach the moderate benchmarks, the standard response is to descend to a lower altitude. Do not treat worsening symptoms as something to push through. Once you hit severe territory, descend immediately and, in the worst cases, call for medical assistance. HAPE and HACE both require getting down and getting help without delay.

What Success Looks Like

A well-managed mountain trip does not necessarily mean zero symptoms. A realistic goal is to keep any illness mild, so you never have to change your itinerary or call for a rescue. If you arrive, sleep a couple of nights in the 8,000 to 9,000-foot range, gain sleeping altitude in small increments above 9,800 feet, and pay attention to how you feel, you give the acute acclimatization process the three to five days it needs.

What has altitude done to you on a hunt, and how did you handle it? Drop your story in the comments below.

The common mistakes are all variations of impatience. Flying straight to a high sleeping altitude on day one, banking on fitness or hydration to carry you, and ignoring mild symptoms as you keep climbing are the errors that turn a manageable adjustment into a cut-short trip or a medical emergency. Denial is itself a severe symptom, so build a habit of honest self-assessment and trust your group to call it when you cannot.

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