Altitude sickness describes several symptoms that happen to your body when you’re exposed to a higher elevation within a short period of time.

Altitude sickness is common when people are traveling and either climbing or being transported to a higher elevation quickly. The higher you climb, the lower the air pressure and oxygen levels get. Our bodies can handle the shift, but they need time to gradually adjust.

Here are some things you can do to prevent yourself from getting altitude sickness.

Your body needs about two to three days of slowly going higher in order to adjust to the changes. Avoid flying or driving directly to high altitudes. Instead, go up higher each day, stop to rest, and continue the next day. If you have to fly or drive, pick a lower altitude to stay at for 24 hours before going all the way up.

When traveling on foot, plan your trip up with stopping points at lower elevations before reaching your final destination. Try to travel no more than 1,000 feet each day, and plan a rest day for each 3,000 feet you go higher.

It’s not often we’re told to eat extra carbohydrates. But when you’re at a higher altitude, you need more calories. So pack plenty of healthy snacks, including lots of whole grains.

Alcohol, cigarettes, and medications like sleeping pills can make altitude sickness symptoms worse. Avoid drinking, smoking, or taking sleeping pills during your trip to higher altitude. If you want to have a drink, wait at least 48 hours to give your body time to adjust before adding alcohol into the mix.

Staying hydrated is also important in preventing altitude sickness. Drink water regularly during your climb.

Climb at a pace that’s comfortable for you. Don’t try to go too fast or engage in exercise that’s too strenuous.

Altitude sickness usually gets worse at night when you’re sleeping. It’s a good idea to do a higher climb during the day and then return to a lower altitude to sleep, especially if you plan on climbing more than 1,000 feet in one day.

Usually medication isn’t given ahead of time unless flying or driving to high altitude is unavoidable. There’s some evidence that taking acetazolamide (the former brand name of Diamox) two days before a trip and during your trip can help prevent altitude sickness.

Acetazolamide is a medication typically used to treat glaucoma. But because of the way it works, it can also help prevent altitude sickness. You’ll need a prescription from your doctor to get it.

It’s also important to know that you can still get altitude sickness even when taking acetazolamide. Once you start having symptoms, the medication won’t reduce them. Getting yourself to lower altitude again is the only effective treatment.

Symptoms can range from mild to a medical emergency. Before traveling to a higher altitude, make sure to know these symptoms. This will help you catch altitude sickness before it becomes dangerous.

Mild symptoms include:

  • headache
  • nausea
  • dizziness
  • throwing up
  • feeling tired
  • shortness of breath
  • faster heart rate
  • not feeling well overall
  • trouble sleeping
  • loss of appetite

If you develop mild altitude sickness, you should stop climbing any higher and return to a lower elevation level. These symptoms go away on their own when you move to a lower altitude, and as long as they’re gone you can start the trip again after a couple days of rest.

Severe symptoms include:

  • more intense versions of the mild symptoms
  • feeling out of breath, even when you’re resting
  • coughing that won’t stop
  • tightness in the chest
  • congestion in the chest
  • trouble walking
  • seeing double
  • confusion
  • skin color changing to gray, blue, or paler than normal

This means your altitude symptoms are more advanced. If you notice any of these, get to lower altitude as soon as possible, and seek medical attention. Severe altitude sickness can cause fluid in the lungs and brain, which can be deadly if left untreated.

It’s hard to predict exactly how your body will react to high altitudes because everyone is different. Your best defense against altitude sickness is not to climb too high too fast and to be prepared by practicing the tips above.

If you have any existing medical conditions, like heart problems, trouble breathing, or diabetes, you should talk to your doctor before traveling to high altitude. These conditions may lead to additional complications if you get altitude sickness.