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Acute Mountain Sickness (Altitude Sickness): Symptoms and Prevention

*I am not a medical professional or a high-altitude mountain guide.  The information provided in this article is not a substitute for the advice of medical professionals or mountain guides.  This article is only meant to share my experiences and to offer my anecdotal observations of Acute Mountain Sickness.  Always listen to the advice of your mountain guides and seek medical attention as soon as possible if you think you are experiencing Acute Mountain Sickness (Altitude Sickness).*

I didn't always understand Acute Mountain Sickness, more commonly known as altitude sickness, until I had experienced it myself. My travel time is precious and once I realized how it could easily ruin a trip, I decided to learn as much as I could about it.  There's something about a dramatic change in pressure on the body that can really wreck what should be an amazing experience.  In scuba diving, the pressure increases and we regularly practice protocols to deal with that increased pressure.  In high-altitude mountain climbing or trekking, the pressure decreases and so does available oxygen. Unlike in scuba, steps to mitigate Acute Mountain Sickness are not routinely embedded in the prep and training for high-altitude adventures.   At high altitude, the combination of decreased pressure and decreased available oxygen in the atmosphere causes our bodies to have a pretty intense response. Adventurers need to plan and  prepare for that.

Acute Mountain Sickness (AMS) has debilitated many fit and experienced trekkers and mountaineers so it’s something that needs to be taken seriously.   What is most upsetting is when people are fully capable of completing a challenging journey, but AMS makes them believe that they lack the physical ability to take it on.  AMS has a way of destroying the confidence of extremely prepared and fit people. It’s vital that hikers understand AMS before embarking on a high-altitude adventure so that they can mentally prepare themselves to recognize and manage the onset of AMS symptoms, but most importantly, so that they can do everything in their power to prevent it.


AMS is not very well understood  by the medical community.  It’s difficult to study and unfortunately, it’s not possible or practical to conduct scientific research during the cases where people are experiencing AMS.  While someone is experiencing horrible, sometimes possibly life-threatening, symptoms they can't be studied because the energy has to be directed at helping them, not studying them.  Even though there is a lack of research on the topic of AMS, there are some common complaints from people who have experienced it. Here are some symptoms you can look out for. 

  • Headache  (this symptom always shows up as part of AMS.  If you don’t have a headache, your symptoms are likely due to some other ailment, not AMS)

  • Nausea/vomiting

  • Diarrhea

  • Intense fatigue

  • Delirium

  • Dizziness/light-headedness

  • Body aches

  • General feeling of being “off”

The role of fitness level in combating Acute Mountain Sickness

In my work as an outfitter and adventure travel coordinator I encounter many people who are preparing for high-altitude trekking or mountain summiting. They're mostly very concerned about fitness.  They spend countless hours training so they are at their peak physical level for the experience.  They wrongly believe that if they are fit enough, then surely, they must have enough cardiovascular stamina to avoid AMS entirely. While it certainly helps to be relatively fit to take on the physical work of a challenging hike, it does not ensure against AMS. In fact, I’ve seen AMS  strike some of the most physically fit adventurers mainly because they fail to prepare for the stress that a high-altitude climb will have on their physiology, and that can have very little  to do with their fitness level. It’s a reality that is hard for some to understand, until they experience AMS for themselves.  


  • Arrive at the starting town a few days earlier.

  • Drink LOTS of water before and during the hike.

  • Use low-sugar electrolyte mixes or salt tablets to stay hydrated.

  • Eat small meals frequently throughout the hike.

  • Keep a slow pace moving up and down in elevation.

Arrive at the starting town a few days earlier.

One of the best things that a high-altitude hiker can do is simply give themselves time to acclimatize.  Spending days at altitude and doing some shorter acclimatization hikes can do wonders to pre-empt AMS. The folks that live at high altitude, of course, don’t suffer AMS because their bodies have adapted to the reduced oxygen available, but for most of us, time to acclimatize by arriving at the start town a few days ahead of a hike will be invaluable.  

I've been guilty of NOT doing this myself.  When my husband and I were in our early 20s we could not afford to fly into a place five days in advance.  We didn’t have enough time off from work and we sure didn’t have extra money to pay for the additional days of accommodation.  We’d land and have to hit the ground running, so acclimatizing in the town ahead of time has always been a challenge for us.   One of our favorite places on Earth is Peru. When we fly into Cusco, we’ve increased our elevation from sea level to 11,000 feet.  That is not a normal experience, and the human body does not know how to handle the sudden loss of pressure and oxygen.  The first time we went to Peru I felt very ill after landing.  I thought that maybe I was catching something because I just did not feel well and I had a nagging headache.  I started drinking lots of water to help with any illness that I might have caught because I was determined not to get sick. Roughly 24 hours after starting to drink lots of fluids I felt back to normal and it dawned on me that I was suffering from Acute Mountain Sickness, not some bug that I caught on the plane.  It was after that trip that I started digging into research about AMS to learn how to avoid it in the future. 

Drink lots of water before and during the hike

Hydrate hydrate hydrate!  Properly hydrating at high altitude is critical.  At high altitudes we lose fluids through our lungs at a higher rate than at sea level, so just breathing during normal activity causes increased fluid loss. People get dehydrated very quickly at high elevations and they may not even realize it.  They reason that they haven't done many activities to cause fatigue and dehydration.  Often, all they’ve done is walk around a market or leisurely strolled for some sightseeing.  The thing is, even though they weren’t exerting themselves or doing anything strenuous, they’ve already put themselves at a hydration deficit, just by breathing at high elevation.  Because of that, once our clients reach our start location,  I always recommend that they rest and chug so much water that it feels like overkill.  That’s when they are probably drinking enough.  

Use low-sugar electrolyte mixes or salt tablets to stay hydrated.

During the hike, it’s not only important to drink lots of water, but to also consume high quality, low-sugar electrolyte fluids, the more concentrated, the better.  The body sheds a lot of electrolytes along with fluids at high-altitude, so concentrated electrolytes and salt tablets can be a hiker’s best friend. I go to a running store before all my trips and get salt tablets so that I can chew on them when we're hiking. I take one tablet an hour and that works well for me.  

Some guides will carry a salt mixture that is more intense than traditional electrolyte additives like Nuun or Liquid IV.  It’s incredibly salty and unpleasant to drink, but it’s also incredibly effective at combating the effects of AMS.  When a guide offers it, I recommend taking it.  It is likely that they are seeing signs of AMS and this salty mixture, although disgusting to drink, will start to ease the AMS symptoms quickly.  I’ve seen it work its magic first-hand.  My mom joined us on a trip to Peru to hike the Inca trail.  On our first day of hiking, she showed symptoms of AMS less than halfway in.  By the end of the hike, the symptoms overwhelmed her and she thought she might need to go to the hospital.  I checked her pack and she had barely drunk a liter of water and had only managed to sip ¼ of the electrolyte drink bottle I had given her early in the hike.  Our guide filled up her water bottle with his special electrolyte mixture and she felt so much better within just an hour or two.  

** A note about alcohol. It’s so tempting to partake in alcohol, especially since many of these high-altitude adventures are trips of a lifetime.  Hikers want to celebrate with fellow journeyers, and a beer or glass of wine can seem harmless. I don’t drink alcohol before or during a high-altitude hike.  Alcohol will contribute to the likelihood of the onset of AMS symptoms.  Alcohol will dehydrate the body and that is already a battle we fight when we are at high altitudes.  I recommend saving alcoholic celebrations for the end of the hike.

Eat small meals, frequently, throughout the your time at altitude.

Digestion slows down quite a bit at high altitude. Blood flow is slower and the body’s ability to digest complex foods diminishes. To keep nausea and other digestive symptoms of AMS at bay, hikers will want to eat several small and simple meals throughout the hike.

Keep a slow pace moving up and down in elevation.

What’s true about acclimatizing at the start of the trip is true during the hike as well.  Hiking upward (or downward) too quickly can trigger AMS. Keeping a slow pace is always recommended, but it is especially critical when acclimatization before the hike could not happen, either because the start of the hike is not at high elevation or because arriving at the start town well in advance of the first day of hiking was not possible.  Slow hikers at high altitude are better off than people who keep a brisk pace because they have taken care to manage AMS.  It’s not unusual to see faster hikers quit or have to be helped off a high-altitude mountain because of AMS.  

When I hiked Kilimanjaro, we started at a pace that seemed comically slow. Unlike other high-altitude hikes, the trek to summit Kilimanjaro starts at a relatively low elevation.  The elevation gain is all on the hike up the mountain. To prevent AMS, acclimatization had to happen entirely on trail. Our guide’s slow pace seemed silly, but I knew it was to prevent AMS symptoms.  Even when starting a trail at high altitude, there is still elevation gain that happens on the hike so keeping acclimatization in mind is crucial.  At the end of my Kilimanjaro experience my group was so grateful that we'd been walking that slowly the whole time because even at that slow pace we were hurting when we reached the terminus. 


***High Altitude De-Acclimatization Syndrome (HADAS) is the same thing as AMS, but in reverse.  Moving from low altitude to high altitude can confuse and stress the body in the form of AMS. When suffering AMS on trail, many hikers may feel that moving back down the mountain quickly will erase the AMS symptoms. And it’s true that moving towards levels of higher oxygen concentration can improve or even get rid of AMS symptoms. However, sometimes descending the mountain too quickly, moving the body from high elevation to low elevation, without de-acclimatizing can trigger HADAS symptoms. HADAS symptoms are very much like AMS symptoms. So, sometimes when a hiker descends a high-altitude mountain quickly to escape the AMS symptoms, they are actually potentially adding to the intensity of their symptoms.

Be prepared and go for it!

High altitude hikes can offer challenging and epic experiences. Understanding how to recognize and manage Acute Mountain Sickness BEFORE you get to the trail will ensure that the glass of wine (or pint of beer or tumbler of non-alcoholic beverage) you lift at the end of the adventure is one that you lift to celebrate a successful journey. Keep Adventuring!

To read more about Acute Mountain Sickness, check out these sources:

My husband is a firefighter-paramedic and I learned a lot of what I know about AMS from his textbook:

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