Hiking at Altitude: Tips for Acclimatization

High-mountain trekking is what dreams are made of: the jagged peaks, rumbling glaciers, and crisp mountain air transport you to another world. The alpine wonderlands of Peru and Nepal draw hikers from all over the world. Massive volcanoes, such as Kilimanjaro and Denali, send out their siren calls to adventure-seekers. Many of these classic treks start in towns or villages at high elevations. You may reach elevations over 15,000 feet. Even hiking destinations such as Rocky Mountain National Park in Colorado or Everest Base Camp in Nepal will have you standing at over 13,000 feet.

If you plan to climb and sleep above 8,000 feet, it is important for you to acclimatize. Once you arrive at your destination, spend time at high-elevations before attempting any serious trekking. While the acclimatization process can delay your hiking plans, it is crucial to allow your body to adjust to the new environment. Take a few days once you arrive at your destination to acclimatize. Go on shorter day hikes, walk around colorful cities, check out a local museum, or taste the country’s cuisine. Integrate “acclimatization days” into your trip itinerary. These pre-planned days will help you stay on track.


What is Acclimatization?

Acclimatization is the process that occurs when your body adjusts to a change in your environment. These physiological adaptations happen gradually, as your body responds to external stimuli. When we are talking about acclimatization, we are talking about high altitude adaptations necessary for you to perform well and stay healthy. If you are planning to travel to a high-altitude destination, give yourself multiple days to rest and perform light activity before your trip.

When you’re hiking at high elevations (over 8,000 feet), it is essential to acclimatize—or become adjusted to the new environment—before you start exerting much energy. You should be gaining altitude at a speed that your body can handle. This speed will differ for everybody. As you reach high elevations, air pressure drops. Oxygen molecules have more room to spread out in the air. With each breath you take in, you’ll be receiving less oxygen than you would at sea level.

Your body will sense the drop in pressure and try to compensate. Breathing becomes labored; your heart thumps rapidly. Your body works tirelessly to produce more red blood cells to deliver the oxygen around your body. But all this takes work—hard work. And if you add in heavy exercise, your body will quickly become overworked and exhausted. It will go into survival mode, suppressing any less-essential bodily functions (such as food digestion).

If you don’t take time to acclimatize before a hiking trip properly, you’ll be at higher risk for altitude sickness. Generally, this happens when a hiker or climber travels too high too fast. However, if you slow down and allow yourself to adjust, you’ll reduce your chance of getting altitude sickness. You will undergo the physiological changes necessary to support the decreased oxygen intake.

The “acclimatization line” will change for each person. Generally, symptoms don’t present below 8,000 or 9,000 feet. The higher in elevation you go, the greater the risk. Acclimatization is a slow and necessary process that takes time: altitude sickness does not discriminate by fitness, age, or experience level.

Altitude Sickness

Altitude sickness results when your body isn’t getting sufficient oxygen due to different conditions at high altitudes. While the percentage of oxygen in the air remains the same across elevations, the barometric pressure changes. Oxygen molecules have more room to spread out, so you’re taking in less oxygen with each breath. And as you travel higher, the pressure drops and the problem worsens.

Altitude sicknesses do not discriminate. It can hit people of any fitness level, age, or experience level. Even if you’ve been to high altitude without problems, there is no guarantee you won’t experience symptoms of altitude sickness the next time. Acute Mountain Sickness (AMS), HAPE, and HACE—all types of altitude sickness—have varying degrees of severity. We’ll cover each one in detail and take a look at the symptoms so you can stay vigilant when traveling to high elevation zones.


Acute Mountain Sickness

Acute Mountain Sickness, which occurs at around 8,000″ and higher, is the most common type of altitude sickness. Mild symptoms include a throbbing headache, dizziness, nausea/vomiting, fatigue, loss of appetite, and trouble sleeping. These symptoms may get worse with heavy exercise and will subside at rest. AMS may worsen at the end of the day, as your respiratory rate slows, and your oxygen intake decreases.


For mild AMS, these symptoms subside within 2 – 4 days of arriving at altitude as your body acclimatizes. If you’re experiencing even mild AMS, you need to take it easy and not gain additional elevation. Descend to sleep lower than the altitude at which you are hiking, if possible. If your symptoms remain mild, you may continue to ascend while monitoring yourself for worsening symptoms.

Even if you’re only displaying mild symptoms, be sure to communicate with your hiking party and monitor your symptoms. Whether you are on a guided trip or a personal excursion, keep your travel mates informed of how you’re feeling. The backcountry is no place to “tough it out.”

Moderate/Severe Acute Mountain Sickness

While AMS is common in the mountains, it can lead to serious problems if you don’t take adequate time to adjust. Moderate AMS symptoms include a headache that does not improve with pain medication, poor coordination (ataxia), increased weakness, and nausea/vomiting. At this point, your activity would be impacted, and you must descend until conditions improve. Wait at least 24 hours at a lower altitude to see improvements before attempting to ascend further.

If you experience shortness of breath at rest, or the inability to walk on your own, your acute mountain sickness has taken a turn for the worse, and you’ve pushed your body too far. A rapid descent to lower elevations is critical, so you don’t risk your AMS turning into HAPE.



High Altitude Pulmonary Edema (HAPE) is a life-threatening form of altitude sickness that results from a buildup of fluid in the lungs. This buildup prevents proper oxygen exchange, putting the body in a hypoxic (oxygen-deficient) state. It is rare, especially when hikers and climbers are acclimatized and frequently monitoring mild AMS symptoms. Usually, HAPE occurs at elevations over 11,000 feet but has been experienced as low as 8,000 feet.


Symptoms of HAPE include shortness of breath at rest, a dry cough, chest tightness, and a feeling of suffocation at night, in addition to other AMS symptoms. These symptoms often don’t present until at least two days spent at elevation. It is often a progression of AMS but can occur without AMS symptoms.

Treatment and Prevention

Monitor your recovery time after exertion. If you’re experiencing prolonged recovery time after your activities, consider descending to lower altitudes. Prevention is the best treatment for HAPE, which occurs after a rapid ascent at elevation.

HAPE requires medical treatment beyond what is available in the backcountry. It requires immediate descent and a rapid evacuation.



High-Altitude Cerebral Edema (HACE) is brain swelling resulting from leakage of fluid into the brain. This is the rarest form of altitude sickness, but the most severe. It generally occurs after two days or more spent at elevations over 13,000 feet but has been reported as low as 8,000 feet.


Symptoms for HACE include decreased coordination (ataxia), disorientation and confusion, memory loss, irritability, and a severe headache. Ataxia can also result from other conditions such as dehydration, hypothermia, and hypoglycemia, so take precautions to prevent these conditions from forming.


Most cases develop as a progression of AMS, which we’ve discussed above. If a mild case of altitude sickness starts to display more severely, take precautions and descend before it advances.

HACE requires immediate descent of at least 3500 feet or until symptoms improve. Anyone experiencing HACE should exert minimal activity, so must be accompanied when descending. HACE patients must be evacuated so they can receive professional medical care in a hospital.

Acclimatization Tips

When Do You Need to Acclimatize?

Anybody traveling to and sleeping at elevations of 8,000 feet and higher should acclimatize before attempting strenuous exercise. The higher you’re going, the more necessary acclimatization is, especially when you surpass 11,000 feet.

Risk Factors

  • If you’ve experienced AMS before, you are likely to again. Give extra priority to acclimatization.
  • If you have pre-existing health conditions, consult your healthcare provider. Take extra precautions if you have cardiac or pulmonary issues or low/high red blood cell counts.
  • If you live at sea level, you are at greater risk than those living at higher elevations.

The First Step: Prevention

Prevention is the most powerful tool you have to stop altitude sickness.

  • Prior to your trip, stay hydrated and well-fueled. Start hydrating 2-3 days before you arrive at your destination.
  • Train before your trek. Increase your cardiovascular capacity with interval training. Train at a high-level so that when you show up, you won’t be exerting yourself at your maximum. If you’re able, train at high elevation.
  • Avoid alcohol as much as possible.
  • Avoid strenuous exercise for 2 – 3 days after arriving at elevation.

Slow Down, Take It Easy

Taking incremental steps to acclimate will put your body in the best position to adjust to its new environment. Slow down, enjoy your journey, and don’t rush the process.

  • Arrive early and give yourself multiple days to adjust before your hike or climb begins. Take this opportunity to participate in a city tour, visit a museum, or go on lower-elevation day hikes.
  • Build up your exercise intensity; keep it light during the first few days at higher altitudes.
  • Slow down, both physically and mentally. Set a slower hiking pace than you normally do, and take breaks more frequently.
  • Keep your expectations reasonable: your peak fitness at home will be different than your high-altitude performance.
  • Climb high, sleep low. We recommend a 3000-foot difference, when possible. If you climb to 15,000 that day, sleep at 12,000.
  • If you go above 10,000 feet, only increase your sleeping elevation by 1,000 feet per day.
  • Check-in with yourself and others. Often, high-altitude hiking involves a higher investment.  This includes international travel, advance trip plans, and other logistics. Problems at high-altitude tend to arise from poor decision-making, rather than a sudden onset of symptoms.

Maintaining your Health and Hydration

If you keep your body in well-fueled and hydrated, you will create the best chance for proper acclimatization.

  • Eat a high-carbohydrate diet at higher altitudes (especially over 12,000 feet). This fast-burning energy is easier for your body to digest. Additionally, carbs utilize less oxygen to break down than fats. No matter what your diet consists of, bring foods that you will enjoy eating. Your body will be working harder and need more calories than usual.
  • Avoid alcohol, sleeping pills, and narcotics, which decrease your respiratory rate. If your respiratory rate falls, your body will take in less oxygen.
  • Keep your ears exposed while you’re hiking unless the weather is unbearable—they are good receptors of air pressure.
  • Stay hydrated. Add electrolyte mix to your water to supplement.
  • Regulate your body temperature to preserve energy. If you sweat or get rained on, change into dry clothes as soon as you get to camp.
  • Don’t sleep during the day. Keep your body moving lightly throughout the day. When you arrive at camp, resist the urge to hunker down in your tent.
  • Cover your skin during the peak daylight hours, and wear sunscreen—you’ll be encountering much more UV radiation than at sea level.


The best treatment for any altitude sickness is immediate descent (and supplemental oxygen). However, with the help of your healthcare provider, you can determine if medication to help acclimatize is necessary for you.

  • Diamox – This medication is not a cure and does not prevent AMS in everyone. However, some travelers opt to take 125mg twice a day (for adults) to prevent altitude sickness. If you do choose Diamox, start your dose the day before ascent and continue until 24-48 hours after you reach your highest elevation. If you take it after the onset of symptoms, take a 250mg dose and continue until a day after your symptoms clear.
  • Dexamethasone is another medication associated with altitude sickness. It is often carried by mountain guides as a treatment for severe AMS, HAPE, or HACE. Dexamethasone should not be used for acclimatization. It is used to reduce symptoms long enough for climbers to descend to lower elevations. It is not recommended except under extreme conditions.

Hike at High Altitudes with a Guide

You shouldn’t skip high-altitude destinations just because you are concerned about acclimatization. Hiking with a guiding company is a great way to ensure that you take the time to acclimate and have first-aid trained professional guides who understand the symptoms of altitude sickness. Wildland Trekking offers guided backpacking trips and portered treks in high-altitude destinations such as PeruNepalEcuador, and Kilimanjaro. In many international trips, we build in acclimatization days full of activities so that your body will be prepared when we hit the trail! These trips are a stress-free, exciting way to hike at high elevations. The tour company handles permits, gear, transportation, meals, and provides a professional guide so you can focus 100% on enjoying your adventure.

Wildland Trekking Hiking Adventures

As the world’s premier hiking and trekking company, Wildland believes in connecting people to fantastic environments in amazing ways. Wildland Trekking Company offers an array of incredible hiking and trekking experiences in 9 states and 11 countries. Read more about our world-class destinations.

To learn more about our guided backpacking trips and all of our award-winning hiking vacations, please visit our website or connect with one of our Adventure Consultants: 800-715-HIKE.

About Hannah Singleton

Hannah is a content strategist, writer, and guide for Wildland Trekking Company. She was born and raised on the East Coast but currently resides in Salt Lake City, UT where she spends her time exploring the wonders of the Rocky Mountain West. You can check out more of her freelance writing at www.hannah-singleton.com.

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