Plan & Prepare

High Altitude Illness

Altitude sickness can sneak up on even the most experienced adventurers. Lack of oxygen at higher elevation can cause symptoms ranging from mild headaches to severe nausea and incapacitation. If someone feels sick at high altitude, assume it is altitude sickness until proven otherwise.

Left unchecked, altitude illness can quickly cause major discomfort during your activities or end your trip altogether. But, with the right understanding and a little preparation, you can reduce your risk of altitude sickness and confidently take your next adventure to new heights.

Symptoms and Description

High altitude illness includes a spectrum of symptoms which result from the body’s inability to adjust to the relatively low oxygen levels at high altitudes. Our atmosphere consists of 21% oxygen at sea level, but as altitude increases, barometric pressure and oxygen concentration decrease. If your body is not used to this “thinner” air, it will struggle to get the oxygen it needs to your muscles, organs, and tissues.

Your body responds to high altitude primarily by increasing your breathing rate to deliver more oxygen to your body. Other normal responses include increased urination; a fast heart rate; swelling of fingers, hands, and feet; and intermittent rapid breathing while sleeping, with brief breath holding spells.

Preventing and managing altitude illness is all about giving your body the time and rest it needs to “acclimate” to lower oxygen levels. This is best accomplished by a gradual graded ascent with rest days. If someone is sick, descend to the last elevation where they felt well to help resolve the symptoms and allow further time to fully acclimate.


  • Headache
  • Nausea and/or vomiting
  • Fatigue
  • Dizziness
  • Rapid heart rate at rest or with mild exertion
  • Worsening shortness of breath at rest, mild exertion, or at night when sleeping
  • Severe headache with change in consciousness
  • Gait imbalance or loss of coordination
  • Confusion and / or altered level of consciousness

Defining Your Risk Category

Your risk of altitude sickness is based on your elevation, rate of descent, and other personal health factors. Consider the following to define your risk category and plan accordingly.

Lower risk

  • No history of AMS in the past and traveling to 8,250’ to < 9,200’ from low altitude in 1 day.

Moderate risk

  • History of AMS and traveling to 8,250 to < 9,200’ from low altitude in 1 day.
  • No history of AMS and traveling to > 9,200’ from low altitude in 1 day.

High risk

  • History of AMS and traveling to > 9,200’ from low altitude in 1 day.
  • Anyone with a history of HACE or HAPE and traveling to > 8,250’.
  • Anyone traveling to > 11,500’ in 1 day from low altitude.

Guidelines for Safe Travel

Keep in mind that symptoms take 6-12 hours to develop on arrival to a new altitude, and are often worse on awakening the next morning. They may continue to worsen over subsequent days. Make a plan, pay close attention to potential red flags, and be proactive about rest and hydration.


  • Stay hydrated and drink extra water during your trip and physical activities as you would on any strenuous type of exertion. Keep in mind that the symptoms of dehydration can be similar to AMS. (see dehydration)
  • Avoid overhydration. Too much water can dilute your body’s sodium levels and result in other problems (see hyponatremia).
  • PACKING LIST: Water bottles, water filtration system

Pace yourself

  • When traveling above 9,900’, do not increase the sleeping altitude by more than 1,600’ per night.


  • Take proactive rest breaks and as-needed during your ascent or while participating in physical activities
  • Take an extra acclimation day (sleeping at same altitude as the preceding night) for every 3,000’ increase in sleeping altitude.

Protect against sun exposure

  • Solar radiation is stronger at high altitude, especially when reflecting off of ice or snow. This can cause symptoms of heat exhaustion or cause severe sunburn. Protect yourself from direct sunlight and bring high SPF sunblock and reapply every few hours, especially after heavy sweating.
  • PACKING LIST: High SPF Sunscreen, hat, sunglasses, etc.

Preparation medications

  • Low risk travelers to high altitude do not require medication for prevention of AMS.
  • Moderate Risk and High Risk travelers, consider over the counter medications (ibuprofen) or prescription medications (acetazolamide) for prevention of AMS.
  • PACKING LIST: ibuprofen or prescription altitude medications
  • If you are taking prevention medications, once you reach the highest altitude and planning on staying there for several days, can stop prevention medications after 2 days at the highest altitude (if feeling well).
  • If persistently feeling unwell at high altitude (with or without prevention medications), descend to the last sleeping elevation you felt well at.
  • Stop prevention medications on the descent.

Acute Mountain Sickness (AMS)

Acute mountain sickness (AMS) is a constellation of symptoms that may range from an annoying headache with mild nausea, to severe sickness with a crushing vice-like headache, vomiting, and debilitating fatigue and dizziness.

Early symptom recognition is important. Symptoms often take 6 – 12 hours to develop on arrival to a new altitude, and are often worse the next morning as overnight the body is breathing slower in a lower ambient oxygen environment.

Keep in mind that acute mountain sickness represents the body’s reaction to less oxygen in the atmosphere, so evacuation to lower altitudes for moderate to severe disease will improve symptoms. Early recognition and early descent before illness worsens could avoid later rescue, as a person who may become progressively sicker and thus unable to walk down the mountain as the disease progresses.

Treatment Options

  • Evacuate to a lower altitude.

Are you or a companion experiencing any symptoms consistent with AMS?

If yes, see medical assessment below.

High Altitude Cerebral Edema (HACE)

High altitude cerebral edema (HACE) presents as a severe form, or end stage, of AMS.

  • HACE results from progressive swelling in the brain that leads to severe headache and eventually altered level of responsiveness that may present as confusion, amnesia, drowsiness, or unconsciousness.
  • HACE may affect the balance center of the brain, so a gait imbalance can result in an inability to walk a straight line or loss of balance.
  • HACE may arise as a progression of AMS symptoms, or in severe cases, present as a rapid deterioration in level of consciousness after rapid ascent without the preceding symptoms of AMS.
  • With any symptoms of HACE, prescription drugs such as dexamethasone and acetazolamide should be given, along with immediate descent.
  • A person who you suspect is suffering from HACE should not be allowed to re-ascend, and as they are altered and unsteady, do not let them descend alone.

Are you or a companion experiencing any symptoms consistent with HACE?

If yes, see medical assessment below.

High Altitude Pulmonary Edema (HAPE)

High altitude pulmonary edema (HAPE) is a disorder which presents with severe shortness of breath arising from an accumulation of excess fluid in the lung tissues and gas exchange spaces.

  • Symptoms usually begin 2 – 3 days after ascent to high altitude, with progressive shortness of breath, cough, weakness on minimal exertion and excessive fatigue. With greater accumulation of fluid there is severe shortness of breath, rapid heart rate, and as the disease progresses, there can be a frothy or bloody cough with crackling or wheezing sounds.
  • A person you suspect has HAPE needs to be recognized early, as this is the most common cause of fatal high altitude illness, and they should descend to the last elevation they felt well at.
  • Minimizing the amount of exertion will decrease the symptoms, so rest, backpack removal, or being carried (and oxygen if available) is ideal. Do not let this person descend alone. A decrease in as little as 1,000 ft (three hundred meters) can lead to an improvement of symptoms. Once asymptomatic, the HAPE patient can (cautiously) re-ascend.

Are you or a companion experiencing any symptoms consistent with HAPE?

See medical assessment below.

Emergency Red Flags

Keep an eye out for the following symptoms. These red flags may be cause for evacuation.

  • Headache
  • Nausea and/or vomiting
  • Fatigue
  • Dizziness
  • Shortness of breath on mild exertion
  • Rapid heart rate at rest or with mild exertion
  • Worsening shortness of breath at rest or at night when sleeping
  • Severe headache
  • Gait imbalance or loss of coordination
  • Confusion and / or altered level of consciousness

See medical assessment below.

Are you concerned about high altitude illness?

Download GOES to launch a digital medical assessment or speak with a wilderness medicine physician.