Altitude sickness: Causes, symptoms, and treatment

Altitude sickness is a disorder caused by being at high altitude, where oxygen levels are low, without gradually getting used to the increase in altitude.

It is also known as acute mountain sickness (AMS), altitude illness, hypobaropathy, Acosta disease, puna, and soroche.

The condition occurs at altitudes higher than 8,000 feet (ft), or 2,500 meters (m). Many ski resorts are located at an altitude of 8,000 ft.

This MNT Knowledge Center article will look at the causes, symptoms, diagnosis, treatment, and prevention of altitude sickness, as well as how to recover.

Fast facts on altitude sickness

At higher elevations, the number of oxygen molecules per breath decreases.

Rising to a high altitude without acclimatizing can cause fluid to build up in the lungs and brain.

Symptoms of altitude sickness include weakness, sleepiness, and lack of appetite.

The main causes are climbing to a great height too quickly or staying at that height for too long.

There are a number of treatments for altitude sickness, but the individual should first slowly descend.


Chest pain
Chest tightness is an indicator that symptoms of altitude sickness are becoming complicated.

The severity of symptoms depends on several factors, including:

the age, weight, blood pressure, and general fitness of an individual

how fast a person climbs to 8,000 ft

the amount of time spent at a high altitude

The primary symptom of altitude sickness is a headache. However, this is also one of the symptoms of dehydration.

For an accurate diagnosis, the individual needs to reach least 8,000 ft and have a headache. They must also demonstrate one of the following signs and symptoms:

lack of appetite, nausea, or vomiting

exhaustion or weakness



pins and needles

shortness of breath upon exertion

feeling sleepy

general malaise

swelling of the hands, feet, and face

The following signs may indicate a more serious presentation of altitude sickness or one of its complications.

Fluid in the lungs can cause the following:

a persistent dry cough, often with pinkish sputum


panting, even while resting

Signs of swelling of the brain include:

a persistent headache that does not respond to painkillers

unsteady gait or clumsiness

increased vomiting

gradual loss of consciousness



Chronic vs. acute

Chronic mountain sickness, also known as Monge’s disease, develops after spending an extended time living at an altitude of over 9842 ft (3,000 m). Acute mountain sickness is experienced shortly after ascending too rapidly to a high altitude.

Couple climb mountain
Altitude sickness occurs when people increase altitude too quickly.

The main cause of altitude sickness is ascending to a great height too rapidly. Climbing too high and staying there for too long may also cause it.

At sea level, the atmospheric concentration of oxygen is approximately 21 percent and the barometric pressure averages 760 millimeters of mercury (mmHg).

Higher altitudes do not change the atmospheric oxygen concentration. However, the number of oxygen molecules per breath decreases.

At about 18,000 ft (5,500 m), each breath contains approximately half of the oxygen found at sea level.

The person has to breathe faster to compensate for the oxygen shortfall, and the heart has to beat faster too. Even though breathing faster raises blood oxygen levels, they do not reach sea level concentrations.

Rising to higher altitudes can also cause fluid to leak from tiny blood vessels, resulting in a potentially dangerous fluid buildup in the lungs and the brain. If a human continues rising to higher altitudes without becoming acclimatized, there is a serious risk of life-threatening illnesses.

The human body needs to adapt to the lower air pressure and decreased levels of oxygen. A gradual progression is therefore needed. This slower climb is known as acclimatization.

The average human body needs from 1 to 3 days to become acclimatized to a change in altitude.

People who do not spend enough time acclimatizing to a new altitude before progressing further have the highest risk of developing altitude sickness.

With less oxygen in the blood, the heart and lungs have to work harder. This raises the pulse and the rate of breathing. More red blood cells are made to enable the body to carry more oxygen. The body responds to a change in altitude by altering blood acidity level, lung pressure, electrolyte levels, and fluid and salt balance.

Chronic mountain sickness appears to have a genetic link. Studies discovered that two genes, ANP32D and SENP1, are more common in people who experience chronic mountain sickness.


If a person has climbed to an altitude higher than 2,500 ft (762 m) and has a headache as well as at least one of the above symptoms, an accurate diagnosis is fairly straightforward.

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