Altitude Sickness: Signs, Prevention, and Fixes

You land in Denver, drive two hours up to Breckenridge, and by dinner you have a pounding headache, zero appetite, and a queasy stomach. You slept fine on the plane and barely drank. So what happened?

You went from about 5,280 feet in Denver to nearly 9,600 feet in Breckenridge in a single afternoon. At that height, the air holds roughly a third less oxygen than at sea level, and your body needs time to catch up. When it cannot, the result is altitude sickness, formally called acute mountain sickness, or AMS.

It is not a sign of weakness, and it is not about fitness. Marathon runners get it. People who live at sea level in Florida, Texas, and California get it on ski trips every winter. Studies of travelers ascending rapidly to around 8,000 feet and above find that roughly 1 in 4 develops symptoms. The good news is that most cases are mild, and a few simple decisions can prevent most of them.

Why thin air makes you sick

At sea level, each breath delivers plenty of oxygen to your blood. As you climb, air pressure falls, so each breath carries fewer oxygen molecules even though the air is still about 21 percent oxygen. Your body compensates by breathing faster and deeper, and your heart beats faster to move oxygen around. Over days, your body produces more red blood cells to carry oxygen more efficiently.

Problems start when you ascend faster than your body can adapt. The low oxygen triggers mild swelling in the brain and fluid shifts that produce the classic symptoms. The risk climbs sharply above 8,000 feet, which is why mountain towns like Aspen (about 7,900 feet), Vail (about 8,150 feet), and Breckenridge (about 9,600 feet) are prime territory. Flying into a high airport and driving straight up to a resort, then hitting the slopes the next morning, is the most common recipe for a miserable first day.

The symptoms to know

AMS usually starts 6 to 24 hours after arrival at altitude, which is why it often strikes on your first night. The hallmark symptom is a headache that responds poorly to ordinary painkillers, plus at least one of the following:

• Nausea or loss of appetite
• Fatigue or weakness out of proportion to your activity
• Dizziness or lightheadedness
• Trouble sleeping, including waking up gasping or feeling breathless
• A general feeling of being hungover, despite not drinking

Mild AMS is uncomfortable but not dangerous, and it usually improves within 24 to 48 hours as you acclimatize, especially if you rest. The mistake most travelers make is pushing through it: skiing hard, drinking alcohol, and sleeping even higher the next night. High-altitude pulmonary edema (HAPE) is fluid in the lungs, signaled by breathlessness at rest, a persistent cough (sometimes producing pink, frothy sputum), chest tightness, and blue lips or fingertips. High-altitude cerebral edema (HACE) is swelling in the brain, signaled by confusion, clumsiness, difficulty walking a straight line, and severe headache or vomiting. Either one is a medical emergency: descend immediately, call 911, and get to the nearest hospital. Do not wait to see if it improves overnight.

Who is most at risk

Anyone can develop AMS, but risk is higher if you:

• Ascend fast. Driving from Denver to a 10,000-foot resort in one day is riskier than spending a night in Denver first.
• Sleep high. Your sleeping altitude matters more than your daytime altitude. Skiing at 11,000 feet and sleeping at 8,000 is safer than sleeping at 10,000.
• Have had it before. A previous bout is the strongest predictor of getting it again.
• Push too hard on day one. Strenuous exercise in the first 24 hours increases symptoms.

Age and fitness, surprisingly, do not protect you. Children can get AMS too, though they may show it as fussiness, poor appetite, and restless sleep rather than a clear headache.

How to prevent it: the plan that works

Climb high, sleep low

The golden rule of mountaineering applies to vacations too: go up gradually, and do not increase your sleeping altitude by more than 1,000 to 1,600 feet per day once above 8,000 feet. For a typical ski trip, the practical version is simple: spend your first night in Denver or another lower town before heading to the resort, and take it easy on arrival day.

Take arrival day off, seriously

Plan your first full day as a rest day, not a ski day. Walk around town, eat normally, drink water, and go to bed early. If you feel fine the next morning, ski. If you still have a headache, rest another day. Most resorts will let you shift a lift ticket by a day, and one lost day beats three ruined ones.

Skip the alcohol, at least at first

Alcohol worsens dehydration, disrupts the already fragile sleep you get at altitude, and depresses breathing. Avoid it on arrival day and the first night, along with sleeping pills and sedatives, which can also slow breathing during sleep at altitude.

Eat carbs, drink to thirst

Your body burns more carbohydrate at altitude, and appetite often drops just when you need fuel. Favor soups, pasta, bread, and other easy carbohydrates over heavy, fatty meals on your first day. Drink enough to keep your urine pale yellow, but do not force gallons: overhydration does not prevent AMS.

Ask your doctor about acetazolamide

For travelers with a history of AMS, or anyone flying straight to a resort above 10,000 feet with no time to acclimatize, doctors sometimes prescribe acetazolamide (brand name Diamox). Taken starting a day before ascent, it speeds acclimatization by stimulating breathing. It requires a prescription, can cause tingling in the fingers and toes, and is not suitable for everyone, so discuss it a couple of weeks before your trip, not at the airport.

What to do if you get it anyway

If mild symptoms appear, stop ascending. Rest, drink fluids, eat something light, and take ibuprofen or acetaminophen for the headache. Most people feel better within a day. If symptoms worsen, or if you develop breathlessness at rest, confusion, or trouble walking, descend at once: even dropping 1,000 to 2,000 feet can be lifesaving, and it is more effective than any medicine. Do not try to tough it out because the hotel is paid for; the severe forms can deteriorate in hours.

The bottom line

Altitude sickness is common, predictable, and largely preventable. Ascend gradually, sleep lower than you play, rest on arrival day, and hold the drinks until you have acclimatized. Treat a persistent headache at 9,000 feet as your body asking for time, not as a failure. Give it that day, and the mountains will still be there tomorrow.

This article is for informational purposes only, not medical advice. Altitude sickness can become a medical emergency. Descend immediately and seek emergency care for breathlessness at rest, confusion, difficulty walking, or a cough producing pink or frothy sputum. Talk to your doctor before a high-altitude trip if you have heart or lung disease, sleep apnea, or a history of altitude illness.