Altitude Sickness: What Exactly Is It?

If you’re lucky enough to have traveled to a high-altitude destination—the Rocky Mountains, the Swiss Alps, Machu Picchu—then you may also be unlucky enough to have experienced altitude sickness.

Altitude sickness, also called mountain sickness, is a term encompassing three distinct conditions that occur at high elevations.

You can think of the Earth’s atmosphere as a blanket of air with elevation measured starting at sea level and increasing from there, Jan Stepanek, M.D., M.P.H., chair of the Aerospace Medicine Program, director of the Altitude & Austere Medicine Clinic and co-director of the Aerospace Medicine & Vestibular Research Laboratory at the Mayo Clinic in Arizona, tells SELF.

Your body becomes accustomed to the level of elevation you usually maintain in this atmosphere—so, where you live most of the time. As you go to higher elevations, the amount of atmosphere pushing down on you from above decreases, and so does the oxygen content of the air. These kinds of changes can bring on symptoms of altitude sickness, which is actually a catch-all term for three separate syndromes, according to the Centers for Disease Control and Prevention (CDC). These conditions span a spectrum of severity.

Acute mountain sickness (AMS) is the mildest and most common form of altitude sickness.

There is no precise starting elevation at which AMS symptoms may kick in, but the CDC notes that around 25 percent of visitors to Colorado who sleep at over 8,000 feet present with signs of this illness. (Colorado’s a high state in more ways than one; its average elevation of 6,800 feet above sea level gives it the highest altitude in the U.S.) Dr. Stepanek notes, however, that people can experience symptoms at lower elevations than this.

Symptoms of AMS include headache first and foremost, nausea, fatigue, lack of appetite, trouble sleeping, dizziness, and shortness of breath, according to the U.S. National Library of Medicine. The headache typically comes on within two to 12 hours after arriving at a higher elevation, with other symptoms to follow. Signs of this condition usually only stick around for 12 to 48 hours, according to the CDC. “[Acute mountain sickness] occurs in many people and typically is not going to cause any serious problems unless you continue to ascend,” Dr. Stepanek says.

Experts don’t know exactly what causes AMS, but the most commonly accepted theory focuses on how quickly increasing your elevation impacts your brain. “There are changes in blood flow to the brain when [you] go to altitude, and this can cause in some individuals an increase in swelling of the brain tissues,” Dr. Stepanek says.

Luckily, the mild symptoms involved with AMS are not usually a reason to worry. According to the CDC, you can descend around 1,000 feet for relief after symptoms set in, or you can safely stay put and treat symptoms with over-the-counter medications such as a nonsteroidal anti-inflammatory drug for a headache or anti-nausea drugs.

You may also find relief through the prescription medication acetazolamide, a drug that helps your body acclimatize to the thinner atmosphere by promoting more efficient respiration, emergency medicine specialist Benjamin Honigman, M.D., professor emeritus and researcher at the Altitude Research Center at the University of Colorado School of Medicine, tells SELF. “It fools the body into thinking that you need to breathe faster and harder because of the way it influences the acidity of the blood,” he explains. Another drug that may help is dexamethasone, the CDC says, a corticosteroid that will rapidly decrease the brain swelling involved here. If you’re not sure how your body will handle higher altitudes, it may be smart to see a doctor before your trip and get these medications just in case.

By the way, it’s a total myth that being young and fit can make you immune to these physiological changes, Dr. Stepanek says. Believing as much can actually be a risk factor of sorts for altitude sickness because people may be more likely to push past their physical limits if they think they’re not susceptible. “The most dangerous thing in the mountains is overconfidence, self-reliance on fitness, and thinking nothing bad can happen,” Dr. Stepanek explains.

AMS can progress into a potentially life-threatening condition called high-altitude cerebral edema (HACE).

HACE is triggered by that same brain swelling on a more severe level. “It starts to impact the ability of blood flow to get to brain tissue, and you start having trouble with your brain being able to function normally,” Dr. Stepanek explains.

A tell-tale symptom distinguishing HACE from AMS is ataxia, or loss of balance, Dr. Stepanek says. Other symptoms include intense fatigue and confusion. As brain swelling continues, it’s possible to lose consciousness and potentially even die. As the CDC notes, this can happen within 24 hours of ataxia settling in if a person doesn’t get to a lower elevation quickly enough.

Treatment means descending ASAP into thicker, higher-pressure portions of the atmosphere—which alone should make you feel better—and seeking medical care immediately, Dr. Stepanek says. You may be treated with oxygen and potentially a drug like dexamethasone, which can even help at high altitudes if you’re not able to descend.

There’s also high-altitude pulmonary edema (HAPE), another potentially life-threatening form of altitude sickness. It can happen on its own or along with AMS and HACE.

HAPE seems to occur when excess fluid collects in the air sacs in the lungs, causing difficulty breathing, according to the Mayo Clinic. “The normally well-distributed blood flow to the lungs starts to get very patchy and cause higher pressure in certain areas of the pulmonary arteries than others,” causing a fluid buildup in your air sacs, Dr. Stepanek explains. It’s a nasty cycle, because as these air sacs fill up, your ability to oxygenate your blood decreases, causing an even greater lack of oxygen.

All of this results in hallmark HAPE symptoms like headaches and excessive shortness of breath with physical exertion, according to the CDC. “Everybody at altitude is going to be a bit short of breath because there’s less oxygen and you’re active, and maybe you’re carrying a pack,” Dr. Stepanek says. But this shortness of breath can quickly become severe and impact you even at rest. Other symptoms include an increased heart rate, heart palpitations, fever, fatigue, chest pain, and a cough that may produce frothy, bloody mucus, according to the Mayo Clinic. Without treatment, this condition can kill even more quickly than HACE, the CDC says.

Treatment involves—you guessed it—descending immediately with as little exertion as possible. If that’s not possible, treatment with supplemental oxygen may be enough, the CDC says, along with drugs such as nifedipine, which acts on your body’s calcium to increase your access to blood and oxygen while easing some of the burden on your heart.

The best way to lower your odds of experiencing any form of altitude sickness is to give your body as much time to adjust as possible before pushing yourself to go higher or exert yourself physically.

The steeper the increase in elevation, the more dramatic of an adaptation your body has to go through. Someone who lives at sea level and flies to 8,000 feet is more likely to get sick than somebody who lives at 7,000 feet and flies up to the same destination, or somebody who lives at sea level and road-trips to their destination over a couple of days.

There may be other factors involved in your propensity for developing altitude sickness. It may well be influenced by a familial or genetic predisposition, Dr. Honigman says. But those factors aren’t well-understood—and, of course, are out of your control. What is in your control: doing your best to let yourself acclimatize gradually.

The CDC advises against going from a low altitude to over 9,000 feet in a single day. Instead, they recommend spending a few days at 8,000 to 9,000 feet before going higher. Then, increase your sleeping altitude by no more than 1,600 feet a day and give yourself a day to adjust for every 3,300 feet of ascension.

Obviously, this can be hard to pull off. “Not everyone has the … luxury of just taking a couple of extra days or weeks of vacation,” Dr. Stepanek says.

If that’s the case, then your best shot is taking it easy to start. The CDC recommends sticking with mild exercise for the first 48 hours of your trip and also not drinking alcohol in that time. (Alcohol can make you pee more, contributing to possible dehydration, and it also has symptoms like loss of balance in common with more serious forms of altitude sickness, which may make the condition harder to spot.)

Definitely back off if you don’t feel good. “Stay hydrated, get good rest, and make sure you don’t overexert yourself,” Dr. Stepanek says. “Be attentive to how you feel, and if you’re not feeling well don’t push it.” Drugs like acetazolamide, dexamethasone, and nifedipine can prevent symptoms of altitude sickness in addition to treating it, the CDC says, so that’s definitely worth bringing up with your doctor if you’re interested.

If you have a heart or lung condition, you may be more at risk for developing altitude sickness, so proceed carefully (and with medical advisement).

“If you have certain heart or lung conditions, then your chances of maladaptation are worse so you have to be more cautious,” Dr. Honigman says. Those include obstructive sleep apnea (when your throat muscles relax and interrupt your breathing as you sleep) and angina (chest pain resulting from lowered blood flow to the heart), according to the CDC.

What’s more, the lack of oxygen at high elevations can accentuate these conditions, even when they are well-managed at sea level.

If you have medical conditions affecting your heart or lungs—or if you don’t, but you’re traveling to a high altitude and are nervous about how you’ll handle it—consult your doctor first. They will be able to explain how high elevations may impact you and may be able to prescribe medications or offer tips so that you can enjoy your trip as safely as possible.

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