The higher you go above sea level, the less oxygen there is to breathe. When you reach elevations above 6,500 feet (2,000 m), your body doesn't always adjust quickly enough to the decrease in oxygen. This can lead to altitude sickness, which is actually a group of potentially life-threatening ailments. Acute mountain sickness (AMS) is the most common type. Other forms of altitude sickness attack the lungs and brain.
Anyone can develop altitude sickness. Not everyone gets it; the effects of altitude vary from one person to the next. Some adjust to the decrease in oxygen more easily than others. But the higher and faster a person climbs, the more likely altitude sickness will develop. About 20% of people who ascend above 8,000 feet (2,500 m) in a day will experience symptoms. Children are the most susceptible. Surprisingly, the risk is twice as high for people under the age of 60 years.
All forms of altitude sickness are caused by low levels of oxygen at very high altitudes. These lower levels result in hypoxia, a shortage of oxygen in the body's tissues. The effects of hypoxia may be mild or even unnoticeable. Altitude sickness is most likely to occur with a rapid increase in elevation, as well as by the cold experienced at high altitudes.
People can adjust to the effects of hypoxia at high altitudes, but only up to a point. At elevations up to 10,000 feet (3,000 m), most people have no problems after a few days. But no one can survive permanently above 17,000 feet (5,100 m). At the elevations reached by mountain climbers, bottled oxygen often becomes necessary.
Risk factors for altitude sickness include:
- abuse of narcotics
- being overweight (although some people do not consider this a risk factor)
- some chronic diseases
- fatigue or overwork
- heavy drinking
Children are especially vulnerable, and can experience high altitude pulmonary edema (HAPE) and high altitude cerebral edema (HACE) below 8,000 feet (2,500 m). Men are five times more likely than women to develop HAPE, but acute mountain sickness (AMS) and HACE affect men and women equally. If someone has had altitude sickness before, they have a three times greater risk. If someone usually lives below 10,000 feet (3,000 m), they are at more than three times the risk of those who reside at higher altitudes. However, if someone lives at a high altitude, an increased risk can develop even after a brief stay at lower elevations.