Altitude Sickness: Causes, Prevention, Symptoms, and Treatment

Many people, after venturing into the mountains for the first time, have experienced altitude sickness. In fact, even people who go into the mountains all the time sometimes still get it. It’s definitely not a fun experience, and can be a little unsettling if you start to get symptoms at the top of a difficult summit.

Fortunately, it’s much less likely to hit you if you take some precautions and pay attention to how your body is responding as you gain elevation.

Since many fly fishermen are also avid hikers, or just like to really get after it when they’re looking for fish, it’s a good idea for anglers to be aware of the possibility of altitude sickness and how to handle it.

If you’re getting ready for a high-altitude adventure of your own, don’t forget to also check out Lightning Safety in the Backcountry.


Acute Mountain Sickness (AMS)

This is the most common form of altitude sickness, and isn’t severe. It can feel similar to a hangover, and doesn’t require immediate medical attention.

High Altitude Pulmonary Edema (HAPE)

This is a serious condition caused by the buildup of fluids in the lungs. It’s much more serious than AMS and could be life-threatening if not treated properly.

High Altitude Cerebral Edema (HACE)

Similar to HAPE, HACE is a buildup of fluid in the brain. It’s the most dangerous of the three types of altitude sickness and needs to be treated as quickly as possible.


At its core, altitude sickness is caused by a change in the air pressure and oxygen level at high elevations. As you climb, the air pressure and oxygen levels drop. If your body isn’t acclimated to these conditions, it can react negatively. It will generally try to compensate for the lack of oxygen by increasing the breathing rate, and although this helps, it often can’t get oxygen levels in the body back to normal.

The likelihood of getting sick increases if you’re exercising vigorously, as your body will be trying to pull in even more oxygen to keep up. Spending a long time at high elevations and ascending quickly also increase the chances of getting sick.

Typically, the risk of altitude sickness starts around 8,000 feet, although it can happen at lower altitudes as well. Even coming to high-altitude cities like Denver or Flagstaff can be a shock to people from sea-level.

Altitude sickness doesn’t discriminate based on age, sex, or physical condition, either. Anyone can experience it. What matters most is whether the body is acclimated to the change in oxygen and pressure. You can be in the best shape of your life and still get it if you climb too quickly.

A sign on a mountain summit reading "Descend Keyhole Route Roll no Rocks"
Altitude sickness can quickly ruin a trip in the mountains.


The best way to prevent altitude sickness is to allow the body plenty of time to acclimate to high elevations. Avoid ascending too quickly or staying at high altitudes for too long. Here are some general guidelines.

  • Avoid smoking and alcohol
  • Stay well-hydrated
  • Ascend slowly and take breaks
  • Avoid strenuous exercise at altitude
  • Eat high-calorie meals
  • On multi-day trips, take rest days as you ascend, and if possible before you start the ascent (think, staying in Denver for a bit before heading into the mountains)

Most cases of altitude sickness can be prevented by stopping, resting, and hydrating at the start of symptoms, and waiting until they’re gone before continuing. Check in with your buddies regularly as you climb to make sure everyone is still feeling good. As long as you pay attention to your body and react accordingly, the likelihood of serious problems is low.


Symptoms generally appear 12-24 hours after getting to high elevation, although more serious cases like HACE can take a while to develop. Knowing what to look for will give you the best chance to fix the problem before it becomes serious. Mild cases of altitude sickness are really similar to a hangover. More serious cases have these, as well as noticeably worse symptoms.

  • Headache
  • Nausea
  • Shortness of breath
  • Vomiting
  • Fatigue
  • Dizziness
  • Tunnel vision
  • Insomnia
  • Decreased appetite
  • Swelling
  • Tightness of chest
  • Bad cough
  • Exhaustion
  • Loss of coordination
  • Confusion
  • Shortness of breath at rest
  • Inability to walk
  • Numbness
  • Hallucinations


Most mild cases of altitude sickness can be resolved easily by catching the problem early and stopping to rest or descending. For more serious cases, though, it might be necessary to seek help and get medications. Treatment depends on the severity of the altitude sickness.


Simple AMS is usually pretty easy to treat. If you notice symptoms, here are some things that can help:

  • stopping and resting
  • descending
  • taking Tylenol or ibuprofen for pain or headaches
  • drinking plenty of water
  • taking it easy and avoiding exercise
  • avoiding smoking and alcohol

HAPE is much more serious than AMS and requires immediate treatment. If you notice symptoms:

  • descend immediately
  • take nifedipine
  • use bottled oxygen
  • seek medical attention
  • descend immediately
  • take dexamethasone
  • use bottled oxygen
  • seek medical attention

Next time you hit the mountains, remember to keep an eye out for symptoms of altitude sickness and stop the problem before it becomes serious. Get your body ready in advance, and know what to look for as you climb. With a little preparation, you’ll have a comfortable, safe, and successful trip in the mountains. If you want more information on all three types of altitude sickness, check out


Leave a Reply