General information

Altitude sickness afflicts around 50% of people who climb to altitudes of 8,000 feet or more. It can be unpleasant, causing headaches and dizziness. Yet, if you know what to expect and how to react to the first signs of altitude sickness, you can often avoid the worst symptoms.

Travelers to Cusco Machu Picchu in Peru often ask questions about altitude sickness. The Inca citadel of Machu Picchu is between 7,000 and 8,000 feet above sea level. Altitude sickness at this elevation shouldn’t be a problem.

What is altitude sickness?

Many travelers to high places have experienced the discomfort of altitude sickness. It is that lightheaded, nauseous feeling you get when you hike up the slopes of a mountain. It usually happens when you climb at a fast pace.

Many people can’t tolerate the lower levels of oxygen and the reduced air pressure that occurs at higher elevations. It takes a while for your body to adjust to these conditions.

Who is at risk for altitude sickness?

Altitude sickness can affect anyone.  50% of people who ascend to altitudes of 8,000 feet above sea level and more will get altitude sickness. Altitude sickness does not respect age, gender, or your state of health. Be on the alert under the following conditions.

  • If you are pregnant, you should talk to your doctor before traveling to high altitude destinations
  • If you suffer from cardiovascular or lung conditions, your doctor may advise you to remain at lower altitudes
  • If you have suffered from altitude sickness in the past, you may need medication to help you to avoid the condition on your next trip
  • You are more likely to suffer from altitude sickness if you live at the coast or other low-level geographic locations. If this is the case, it’s a good idea to arm yourself with information on the symptoms and treatment of altitude sickness.

At what elevation is altitude sickness most likely?

Altitudes over 8,000 feet can bring on the symptoms of altitude sickness. We categorize altitudes as follows:

  • High altitude: 8,000 to 12,000 feet above sea level or 2438,4 to 3657.6 meters above sea level
  • Very high altitude: 12,000 to 18,000 feet above sea level or 3657.6 to 5486.4 meters above sea level
  • Extremely high altitude: any altitude over 18,000 feet or 5486.4 meters above sea level.

Let’s put that into perspective

  • The capital of Peru, Lima City, is 33 feet above sea level
  • Arequipa or Machu Picchu named the “Mile High City” is between 7,000 and 8,000 feet above sea level
  • The Colca Canyon is 10600 feet above sea level
  • Cusco is 10,990 feet above sea level
  • The highest Peruvian town, La Rinconada, is 16,700 feet above sea level.
  • Mount Everest summits at over 29,000 feet.

Categories of altitude sickness

AMS acute mountain sickness, is the most common form of altitude sickness. Up to three-quarters of people who ascend to heights of more than 10,000 feet will experience mild symptoms of AMS.

AMS falls into three categories

  • Mild AMS – this shouldn’t impede your usual activities since it causes only a mild headache and tiredness. If you stay at this height, your body will quickly adapt with the symptoms clearing after a few days.
  • Moderate AMS – at this level you may start to battle with coordination. You may also experience nausea and an acute headache. Only a descent to a lower level will ease the symptoms.
  • Severe AMS – at this level, you will have difficulty walking and may be short of breath even when resting. You must descend as soon as it is safe to do so and seek medical advice as soon as possible.

There are two other forms of altitude sickness. Though infrequent they are more severe. These can result in death so it is absolutely vital that the sufferer descends and seeks immediate medical intervention. These severe forms of altitude sickness include:

  • HACE (High-altitude cerebral edema) – high altitudes cause a surplus of fluid on the brain, causing it to swell. The result may be confusion, uncoordinated movement, and even violent behavior.
  • HAPE (High-altitude pulmonary edema) – high altitudes cause surplus fluid in the lungs. The result is shortness of breath, weakness, and fatigue. It may feel as though you are suffocating as the fluid fills your lungs.

The cause of altitude sickness

As you climb to higher elevations, the air pressure and oxygen levels drop. Your body needs time to adapt to these changes even if you are physically fit.

Though scientists don’t understand why it happens, low air pressure and high altitude can cause fluid to leak out of your blood vessels. The fluid from your vessels accumulates in your brain and lungs. Failure to take action when you experience moderate to severe symptoms of altitude sickness could put your life at risk.

Recognizing the symptoms of altitude sickness

Symptoms differ according to the level of altitude sickness that afflicts you.

Mild, short-term altitude sickness

Symptoms usually start between 12 and 24 hours after you arrive at your high-altitude destination. As your body adjusts over the next day or two, the symptoms will ease. Symptoms include:

  • Dizziness
  • Loss of energy
  • Shortness of breath
  • Loss of appetite
  • Problems with sleep.

Moderate altitude sickness

Symptoms of moderate altitude sickness are more severe. Rather than improving over time, symptoms tend to worsen. They include:

  • Worsening fatigue, shortness of breath and weakness.
  • Difficulty with coordinated movements
  • Nausea, vomiting, and an acute headache
  • A tight chest or congestion
  • You may still be able to walk without assistance but regular activities become more difficult.

Severe altitude sickness

Severe altitude sickness is a health emergency and requires immediate descent and medical intervention. Though it appears that the symptoms are the same as moderate AMS, they are more extreme. You must move to a lower altitude as soon as you experience these symptoms and seek medical care:

  • Shortness of breath, even when resting
  • Inability to walk
  • Confusion
  • Accumulation of fluid on the lungs or brain.


The movement of oxygen through your body is impeded by the accumulation of fluid in the lungs. The symptoms of HAPE include the following

  • Weakness and intense tiredness
  • Cyanosis, during which the nails, lips, and skin start to turn blue
  • A tight chest and difficulty breathing even when at rest
  • An incessant cough issuing watery sputum
  • Irrationality and confusion
  • Night time suffocation.


When fluid leaks into the brain, the brain swells and you need immediate medical help. The symptoms of HACE include

  • Loss of memory, disorientation, and hallucinations
  • Weakness and the inability to coordinate movement
  • Psychosis


The first symptom of altitude sickness is a headache. If the headache is accompanied by at least one other symptom, and you have moved to a higher altitude in the past two days, the likely cause is altitude sickness. Experienced climbers will recognize the signs of altitude sickness.

The doctor may order chest X-rays if he or she suspects that you may have fluid on your chest. An MRI or CT scan can confirm the presence of fluid on the brain.

The management and treatment of altitude sickness

The first and most obvious treatment of altitude sickness is the removal of the patient to a lower altitude as quickly as possible. If you have mild symptoms, you may choose to wait it out. Staying where you are may help to acclimatize your body to the conditions.

As with most illnesses, the treatment depends on the severity of the condition

  • Mild altitude sickness – treat the headache with over-the-counter painkillers. As your body adjusts to the conditions, any other symptoms will disappear.
  • Moderate altitude sickness – descend by 1,000 to 2,000 feet to alleviate the symptoms. It should take no more than three days for the symptoms to completely disappear.
  • Severe altitude sickness, HACE and HAPE – If your symptoms are severe, you will have to move down to an altitude lower than 4,000 feet. You need medical attention and may require hospital treatment.

Preventing altitude sickness

You can avoid altitude sickness by taking it slowly. A slow ascent helps your body to acclimatize to the reduction in oxygen levels as you rise.

Speak to your doctor about taking acetazolamide. Taken 24 hours before the ascent and for five days during the trip, will reduce the symptoms of altitude sickness. Dexamethasone is also sometimes used as a preventative measure, but it can have nasty side effects.

You can avoid the worst symptoms of altitude sickness by listening to your body. When you start to feel ill, slow your ascent or descend to lower altitudes. You will quickly recover.

Though rare, altitude sickness can cause life threatening conditions. Left untreated, HACE or HAPE can result in coma or death. Speedy medical treatment is necessary.

How to acclimatize your body to higher altitudes

It is possible to acclimatize your body to higher altitudes and avoid altitude sickness.

  • Walk – Start your climb at less than 10,000 feet. Rather than driving or flying, take a walk. If you have driven or flown to an altitude of more than 10,000 feet, spend 24 hours getting used to the conditions before you continue the climb.
  • Keep it slow – don’t climb more than 1,000 feet per day once you have reached 10,000 feet.
  • Take a rest – take a day off from climbing every 3,000 feet of ascent
  • Sleep at a lower elevation – if you have made an ascent of more than 1,000 feet in the past day, move down to sleep.
  • Look out for the signs of altitude sickness – take action as soon as you start to feel symptoms. Start a descent or, at the very least, stop climbing.
  • Carb up – ensure that your diet includes at least 70% carbohydrates.
  • No drugs or tobacco – avoid tranquilizers, sleeping tablets or tobacco
  • Stay hydrated – you need between 3 and 4 quarts of water every day. Avoid alcohol. It will dehydrate you and impact your judgment.

What you should do if you’re planning to travel to high altitudes

If you’re planning a high-altitude holiday, find out whether there are any medications that can help you to prevent altitude sickness. This is particularly important if you have had altitude sickness before or if you are at high risk of developing the illness. Knowledge and preparation will help you to deal with the symptoms, preventing them from escalating and spoiling your holiday. You should not have to acclimatize during your Peru, Machu Picchu climb. Your guide can help you with information on altitude sickness in Peru.

About the Author
I am Boris Rojas is one of River Explorers owners and author of all the texts you find on the website and on social media. With my blog posts, I hope that you will learn more about Peru and be inspired to SELF to start arranging YOUR OWN unforgettable journey to the ancient kingdom of the Incas! See you on the blog, on Facebook, and maybe even "in real life".

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