Altitude sickness is a general term encompassing several disorders that occur high altitudes. High altitude is greater than 8,000 feet; medium altitude is between 5,000 and 8,000 feet; and extreme altitude is greater than 19,000 feet. There are groups of people who have lived at high altitudes for generations, and they are simply accustomed to living at such altitudes. However, people who are accustomed to lower altitudes are at risk of developing altitude sickness.

Most healthy individuals suffer altitude sickness at very high altitudes. About 20% of people ascending above 9,000 feet in one day will develop altitude sickness. Individuals with preexisting medical conditions--even a minor respiratory infection--may become sick at more moderate altitudes.

Altitude sickness occurs because the air contains less oxygen at higher altitudes. Therefore, there is a lower amount of oxygen for an individual to breathe. This is known as hypoxia. Furthermore, since there is less oxygen to inhale...