Acute mountain sickness, or AMS, is a mild, self-limiting form of altitude illness. Altitude illnesses are caused by lack of oxygen as a person climbs to higher altitudes. A more severe form of altitude illness, known as high-altitude cerebral edema or HACE, has much more serious consequences.

What is going on in the body?

As altitude increases, the atmospheric pressure decreases. There are fewer oxygen molecules available. This decrease in oxygen availability affects the body in many ways. The rate and depth of breathing increase. This disturbs the balance between gases in the lungs and the blood. This imbalance causes changes in the distribution of potassium and sodium in the cells. As a result, water is distributed differently between the blood and the tissues. This change in distribution causes the effects of altitude illness.

What are the causes and risks of the condition?

Acute mountain sickness can happen with steady climbs to higher altitudes. It can be prevented by climbing gradually and getting used to midway altitudes. Some people will have symptoms after rapid climbs from sea level to 8,000 to 10,000 feet. Climbers from sea level to 14,000 feet almost always have symptoms. AMS is more common in younger adults than in older people. Individuals with history of AMS and those with lung diseases are more prone to this condition.