What is altitude sickness?

Altitude sickness occurs when you cannot get enough oxygen from the air at high altitudes. This causes symptoms such as a headache, loss of appetite, and trouble sleeping. It happens most often when people who are not used to high altitudes go quickly from lower altitudes to 8000 ft (2438 m) or higher. For example, you may get a headache when you drive over a high mountain pass, hike to a high altitude, or arrive at a mountain resort.

Mild altitude sickness is common. In the United States, more than 20% of people visiting the western mountains get it.¹ Experts do not know who will get it and who will not. Being male or female and your fitness level play no role in whether you get altitude sickness.

Altitude sickness can be dangerous. It is smart to take special care if you go high-altitude hiking or camping (like in the Rockies) or have plans for a vacation or trek in high-altitude countries like Peru, Ecuador, or Nepal.

Altitude sickness is also called acute mountain sickness.

What causes altitude sickness?

Air is "thinner" at high altitudes. When you go too high too fast, your body cannot get as much oxygen as it needs. This causes the headache and other symptoms of altitude sickness. As your body gets used to the altitude, the symptoms go away.

What are the symptoms?

The symptoms of altitude sickness include:

• A headache, which is usually throbbing. It gets worse during the night and when you wake up.
• Not feeling like eating.
• Feeling sick to your stomach. You may vomit.
• Feeling weak and lazy. In severe cases, you do not have the energy to eat, dress yourself, or do anything.
• Waking up during the night and not sleeping well.
• Feeling dizzy.

Your symptoms may be mild to severe. They may not start until a day after you have been at a high altitude. Many people say altitude sickness feels like having a hangover.

Altitude sickness can affect your lungs and brain. When this happens, symptoms include being confused, not being able to walk straight (ataxia), feeling faint, and having blue or gray lips or fingernails. When you breathe, you may hear a sound like a paper bag being crumpled. These symptoms mean the condition is severe. It may be deadly.

If you are going on a high-altitude trek, learn about altitude sickness, its symptoms, and how to treat it. Look out for other people in your group. You can learn more about altitude sickness at the International Society for Mountain Medicine website at www.ismmed.org.

How is altitude sickness diagnosed?

If you are at a high altitude, your doctor may think you have this condition. Your doctor will ask you questions about your symptoms and examine you. To rule out other conditions, your doctor may ask if you have been drinking fluids or alcohol or using any medicines, or if you have a cold or the flu.