Altitude Sickness: What Is AMS and How Do I Avoid It?

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Ever been on a hike and suddenly felt nauseous? There’s a high chance you were experiencing altitude sickness. More commonly known as acute mountain sickness (AMS), It is caused by lower oxygen and air pressure levels at higher elevations.

Most people will recover as their body becomes accustomed to the higher altitude. However, if left untreated, AMS can develop into a life-threatening situation. Learn the symptoms, and how you can prevent them from occurring. 

What Is AMS and How Do I Avoid It

What is Altitude Sickness?

Altitude sickness typically occurs at heights around 8,000 feet. However, it can expedite with activity levels, speed of elevation increase, and individual factors. It is important to climb at a steady rate to acclimatize properly so that we allow our bodies to adjust to a new environment.

Anybody can be affected. One’s age, gender, or physical fitness level does not impact their ability to experience altitude sickness. Furthermore, those who have never been to a high altitude location might experience symptoms quicker than those who have. 

Altitude sickness is very common, and more than half of people who climb to higher elevations experience it. 8,000 feet may seem very high but many cities and countries around the world already sit at a certain height. 

Popular destinations like Machu Picchu in Peru, and Shangri-la city in China, sit at 8,000 and 9,000 feet respectively. Furthermore, countries like Colombia, Nepal, and most of Switzerland, already reside at heights at or more than 8,000 feet.

Travellers can expect to feel some discomfort upon arrival. Especially if they have never experienced high altitudes before. It is important to be aware that altitude sickness can result in severe symptoms if left untreated. Make sure to give yourself ample rest as even the mildest of symptoms can take a few days to subside.

Causes of Altitude Sickness

Causes of Altitude Sickness

The leading cause of AMS is ascending to high altitudes too quickly. Consequently, staying at those elevations for extended periods of time can also cause further complications such as chronic mountain sickness.

The oxygen concentration at sea level is around 21%, with an air pressure of around 760 mm hg. However, at higher altitudes, this air pressure drops. For example, Mount Everest’s peak has an air pressure of around 228 mm hg. When air pressure lowers, there are fewer oxygen molecules in the air. 

Because our body needs oxygen to survive, this makes it harder to breathe. Shortness of breath is a strong sign that air pressure is low. When there is less oxygen in our body, our heart and lungs work harder to compensate. 

It usually takes 1 to 3 days for the human body to acclimatize to changes in altitudes. Not spending enough time adjusting results in symptoms appearing.

Signs and Symptoms of Altitude Sickness

Signs can show as early as 12 hours and can last up to 3 days. Feeling any of the following should result in resting and assessing symptoms:

  • Dizziness
  • Fatigue and loss of energy
  • Shortness of breath
  • Loss of appetite
  • Inability to sleep

Moderate symptoms include: 

  • Weakness, and worsening of fatigue
  • Increase in shortness of breath
  • Severe headache, nausea and vomiting
  • Chest tightness and congestion
  • Coordination problems and difficulty walking

Feeling intense symptoms for extended episodes requires medical attention. Not treating AMS properly can result in HAPE and HACE. 

High Altitude Pulmonary Oedema (HAPE)

With HAPE, fluid builds in the lungs preventing oxygen from flowing properly. Symptoms include:

  • Cyanosis, when skin, nails, and the whites of your eye, start to turn blue
  • Confusion and irritable behaviour
  • Tightness in the chest
  • Inability to breathe, suffocating feeling at night
  • Extreme fatigue and weakness
  • Persistent coughing that brings up watery, white fluid

High Altitude Cerebral Oedema (HACE)

HACE happens when brain tissue leaks fluid and swells. Symptoms include:

  • Headache
  • Loss of coordination and disorientation
  • Weakness
  • Psychotic behaviour, hallucinations, and memory loss
  • Comatic episodes

Who is at risk of altitude sickness?

Age, sex, and health do not affect your ability to get acute mountain sickness (AMS). However, you may have a higher risk if the following applies to you:

  • Existing lung or heart condition 
  • Pregnant
  • Never been to high elevations
  • Have experienced AMS before

It is important to contact your doctor or provider prior to travelling to high altitude locations if these conditions apply to you. 

How to Prevent Altitude Sickness

How to Prevent Altitude Sickness

If you are planning to hike to high elevations, it is important to acclimatize properly. These 7 tips will help you do so:

  • Walk to higher elevations
    Driving or flying to heights greater than 10,000 feet is too fast for your body to adjust. 
  • Climb gradually
    Pass the 10,000 feet mark. Try not to ascend more than 1,000 feet per day.
  • Rest more
    Have a rest day every 3,000 feet, and make sure to stay put at least 24 hours past the 10,000 feet mark.
  • Sleep lower
    If you climb more than 1,000 feet a day, try to sleep at a lower altitude.
  • Listen to your body
    Learn and recognize the symptoms of AMS. Identify them early, and treat them accordingly.
  • Stay hydrated
    At high altitudes, our body can alter its fluid and salt balance. Ensure you are drinking enough water and electrolytes.
  • Eat more 
    Fatigue and weakness can kick in faster when your body doesn’t have enough energy. Avoid smoking and drinking alcohol as these will increase shortness of breath, and dehydration accordingly. 

What to eat at high altitudes?

Our bodies are less efficient at higher altitudes compared to sea level. It is essential to increase energy intake through good quality carbs. These are some foods you can bring with you that are perfect for the job:

  • Dates
  • Bananas
  • Sweet potatoes
  • Oats
  • Rice

Avoid refined carbs and sugar as your source of energy. These will make you sluggish and are less efficient fuel sources for your body.

Increase your intake of iron rich foods to help promote red blood cell production. This helps combat the lower air pressure at higher altitudes. Animal protein such as tuna, salmon, lean beef, and chicken contain good amounts of iron. Taking iron supplements can also help.

Increasing your intake of foods high in potassium is an electrolyte that aids your body in fighting stress at higher altitudes. It also helps regulate fluid balance, reduce blood pressure and water retention levels. 

At high elevations, our body works harder. Thus, It is important to protect your immune system. Antioxidants and anti-inflammatory foods will provide your body with the vitamins and minerals needed. Choose colourful foods like the following:

  • Red Strawberries
  • Orange Carrots
  • Yellow Bell Peppers
  • Green Leafy Vegetables
  • Blueberries
  • Purple Eggplant
  • Brown Mushrooms
  • White Cauliflower

Altitude Sickness Diagnosis

Diagnosis can be done based on symptoms, assuming no other health conditions were present. However, once HAPE and HACE are a concern, an MRI or CT scan may be needed to check for fluid present in the brain. 

Altitude Sickness Treatment

Altitude Sickness Treatment

Mild AMS can be treated by resting a few days and allowing the body to acclimatize. If symptoms persist, consider descending to lower elevations. Over the counter medications are also available, and can help relieve symptoms. 

When symptoms are very severe, hospitalization is usually necessary in order to prevent HAPE and HACE from happening. 


These medications can help with mild AMS, and are useful when travelling.

  • Ibuprofen and paracetamol for headaches
  • Anti-sickness medicine such as promethazine for nausea
  • Acetazolamide to prevent and treat high-altitude sickness

Anti-sickness medicine are antiemetic drugs that are usually taken orally to help ease feelings of nausea or vomiting. They work by blocking the signals the brain gives when feeling ill to decrease the severity of symptoms. 

Keep in mind that medication only slows down the process of AMS. If symptoms start to become worse, you might need to descend slightly or rest for a day or two. 

A common medication used by climbers is acetazolamide. It works by increasing the amount of oxygen in the blood. This speeds up the process of acclimatization. 

Acetazolamide should be taken 1 to 2 days before you start climbing. It can also be taken continuously while climbing. However, it is not recommended for those with kidney or liver problems.

In addition, make sure to always consult a doctor before taking any form of medication. 


A person can prevent altitude sickness by ascending slowly. Give the body ample time to properly adjust. Make sure to listen to the signs and symptoms.

These will help you avoid severe life-threatening situations. Taking precautions and planning ahead will benefit you, and allow for a much more fulfilling journey.