Avoiding Altitude Sickness: How to Enjoy the Mountains Safely

At last, you’ve arrived in Cuzco, Peru — you’re ready for your dream trek to Machu Picchu. There’s just one problem: You can barely catch your breath, your stomach is churning and, in the morning, your head is throbbing.

The culprit? Altitude sickness, or in medical terms, acute mountain sickness — the various symptoms tied to your body’s response to the higher altitude. As elevation increases, air pressure drops, meaning you get less oxygen from each full breath. It is temporarily uncomfortable for most people, but in extreme cases, severe altitude sickness can even be fatal.

It sounds scary, but as Paul Nicolazzo, the president of Wilderness Medicine Training Center said, “There’s really no reason to be afraid of going to altitude, as long as you understand what you’re up against, and you obey some very, very basic rules.”

Know the symptoms

A.M.S. has four general symptoms: headache, gastrointestinal discomfort (nausea and lack of appetite), fatigue/weakness, and dizziness/lightheadedness.

Many people experience the morning altitude headache, in which “your skull feels too small for the pulse that’s coming,” said Steve House, the founder of Uphill Athlete, a company that offers high-altitude endurance coaching.

It is also common to struggle with sleep at high altitudes. This occurs partly because the part of your nervous system responsible for keeping you awake has kicked in to increase your respiratory rate, Mr. Nicolazzo said.

Pay attention to elevation

The two main drivers of A.M.S. are how high you’re going and how fast you’re getting there. People with a higher altitude sensitivity might start experiencing challenges not far above 5,000 feet, say in places like Denver and Johannesburg. Anyone traveling above 8,000 feet may be at risk for altitude sickness, according to the Centers for Disease Control and Prevention.

Serious adventure travelers — say, those trekking in the Himalayas, or climbing Mount Kilimanjaro — usually know they’re headed for high altitudes. But the elevation of destinations like Mexico City (about 8,000 feet), the summit of Haleakala on Maui (10,023 feet), Cuzco (about 11,150 feet), or even Santa Fe, N.M. (6,996 feet), might come as a surprise. To set expectations, check your destination’s altitude in advance on Google Earth or the U.S. Geological Survey national map viewer.

Listen to your body

If you have a condition like heart disease, heart failure, high blood pressure, high cholesterol, atrial fibrillation, lung disease, C.O.P.D., asthma or sleep apnea, you’ll want to start paying close attention to how you’re feeling at around 5,000 feet.

If you have a pre-existing condition or have had trouble with high altitudes before — or if you’ll be going above 10,000 feet — consider visiting a specialist, who can help you prepare and may be able to advise you about the main drugs used to prevent and treat altitude sickness, Diamox (acetazolamide) and dexamethasone.

Sleep your way up

Traveling to high altitudes is a little like running a marathon: It will go better if you build up to it.

Say you’re headed to a high-altitude ski resort. Consider working your way up from a lower sleeping elevation to a higher one, since the critical factor — for altitude purposes — is where you spend the night.

If you’re traveling from sea level to Breckenridge, a Colorado ski town that sits at about 9,600 feet, first spend a night in Denver, at 5,280 feet, advised Dr. Peter Hackett, the founder of the Denali Medical Research Project and a high-altitude specialist. By doing so, he explained, “you drop the incidence of headache by almost half. So that little bit of extra time that you take to get to 9,000 feet to sleep can make a big difference.”

Skip that fatty steak

When Mr. Nicolazzo worked as a ski patroller, there was a behavior so common — and certain to exacerbate altitude illness — he remembers that local lodges posted warnings about it. People would fly in from sea level, he recalled, drive to Taos, N.M. (6,969 feet), “have a big steak, baked potato with sour cream and a lot of butter,” along with several cocktails. Then, they would feel terrible the next day, he said.

To avoid that feeling, trade the steak and extra butter for something with more carbohydrates, as fats and proteins take more oxygen for your body to metabolize.

And if you’re having a cocktail, keep it to one: Alcohol and other depressants can decrease your oxygen level, particularly while you’re sleeping, Dr. Hackett said.

Above all, drink plenty of water. Staying hydrated will help your kidneys work better, Mr. Nicolazzo explained, which can help you adjust to the altitude and, hopefully, avoid the headache.

Watch for red flags

A mild case of A.M.S. can become moderate or severe if someone ascends too high or too fast. Most — but not all — people progress through the mild symptoms before reaching this level, which includes symptoms like dizziness, disorientation, severe nausea and extreme shortness of breath.

To guard against severe A.M.S., monitor how you feel, and if you’re experiencing a persistent headache, trouble sleeping or other A.M.S. symptoms, tell your companions and don’t ascend any higher.

At the severe end of the continuum, if not treated, A.M.S. could progress into high altitude pulmonary edema, in which fluid builds up in the lungs, or more rarely, high altitude cerebral edema, where fluid builds up in the brain. Both conditions can be fatal.

“There are three cures for altitude illness,” Mr. House said, “descent, descent and descent.” Anyone who appears confused, is coughing up fluid or seems to have trouble breathing or walking — symptoms of severe conditions like HAPE or HACE — needs to be taken down immediately, Dr. Hackett said. “Just a thousand feet is all they have to go. And that could save their life.”