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1. What is high altitude or mountain sickness?

Sometimes people get sick at high altitudes. This is called mountain sickness or high altitude sickness.

2. What causes high altitude or mountain sickness?

Lack of oxygen causes high altitude sickness. As altitude increases, the air becomes “thinner,” which means less oxygen is in the atmosphere. You take in less oxygen to your lungs with each breath, so the amount of oxygen in your blood declines (this is called hypoxia). Anyone can experience mountain sickness, but it may be more severe in people who have heart or lung problems.

3. What are the symptoms of high altitude or mountain sickness?

Symptoms usually begin within 48 hours of arriving at high altitude. The higher the altitude, the greater the effects.

Symptoms include:
- Headache, breathlessness, fatigue
- Inability to sleep
- Nausea or vomiting
- Swelling of the face, hands and feet

Both heart rate and breathing rate increase as the body tries to send more oxygen to its tissues. At very high altitudes, body fluid can leak into the brain (called brain or cerebral edema) or into the lungs (pulmonary edema). Both of these conditions can be serious or even life-threatening.