What is Altitude Sickness

Dr. Lindsey Nelson explains.

Altitude sickness

—also known as acute mountain sickness (AMS), is a medical problem when we are exposed to high altitude low partial pressure of oxygen usually following a rapid ascent to an elevation above 8,000ft  (82400m).   Common symptoms of altitude sickness resemble the ordinary flu or feeling “hung-over”.   Therefore, people with AMS frequently complain of headache, fatigue, upset stomach, dizziness, and restless sleep.  Furthermore, it is hard to determine who will be affected by altitude sickness, as there are no specific factors that correlate with a susceptibility to AMS.    Anyone who travels to altitudes of over 2500m or 8,000ft is at risk of acute mountain sickness. Normally it doesn’t become noticeable until you have been at that altitude for a few hours. Part of the mystery of acute mountain sickness is that it is difficult to predict who will be affected. It is not uncommon to hear stories of young athletic individuals being badly limited by symptoms of AMS while older members doing the same activity have felt fine.   Do NOT be fooled by AMS or take it lightly. The dangers of this illness can be severe and every year people die of this physiological derangement when left unrecognized and untreated as AMS can progress to the potentially fatal high altitude pulmonary edema (HAPE) or high altitude cerebral edema (HACE).


What causes altitude sickness?

Two things are certain to make altitude sickness very likely – ascending faster than 500m per day, and exercising vigorously.   This includes the many people that come to Colorado on vacation to enjoy our outdoor activities.   Utilizing one of the outdoor “toys” at Rocky Mountain Adventure Rentals, LLC will potentially allow you a quicker ascent than was possible before.  REMEMBER: Physically fit individuals are not protected – even Olympic athletes get altitude sickness. Altitude sickness happens because there is less oxygen in the air that you breathe at high altitudes.  As you may have noticed, you may feel more parched at our altitude so it is also likely, that dehydration due to the higher rate of water vapor loss at higher altitudes may contribute to the symptoms of AMS.

The AAAs that influence AMS susceptibility

  • Ascent Rate
  • Altitude Attained
  • Activity Amount

The Three Forms of Altitude Sickness

Acute Mountain Sickness (AMS)

Mild altitude sickness is called acute mountain sickness (AMS) and is quite similar to a hangover – it causes headache, nausea, and fatigue. This is very common: some people are only slightly affected, others feel awful. However, if you have AMS, you should take this as a warning sign that you are at risk of the serious forms of altitude sickness: HAPE and HACE. Both HAPE and HACE can be fatal within hours.

  • Lack of appetite, nausea, or vomiting
  • Fatigueor weakness
  • Dizzinessor lightheadedness
  • Peripheral edema(swelling of hands, feet, and face)
  • Insomnia
  • Pins and needles
  • Shortness of breath upon exertion
  • Nosebleed
  • Persistent rapid pulse
  • Drowsiness
  • Excessive flatulation
  • General malaise


HAPE is excess fluid on the lungs, and causes breathlessness. It is similar to when people with heart disease are in failure and have pulmonary edema.  It is NEVERnormal to feel breathless when you are resting – even on the summit of Everest. This should be taken as a sign that you have HAPE and may die soon. HAPE can also cause a fever (a high temperature) and coughing up frothy spit. HAPE and HACE often occur together.   DESCEND IMMEDIATELY!!

Pulmonary edema (fluid in the lungs)

  • Symptoms similar to bronchitis
  • Persistent dry cough
  • Fever
  • Shortness of breath even when resting


HACE is fluid on the brain. It causes confusion, clumsiness, and stumbling. The first signs may be uncharacteristic behavior such as laziness, excessive emotion or violence. Drowsiness and loss of consciousness occur shortly before death.  DESCEND IMMEDIATELY!!

Cerebral edema (swelling of the brain)

  • Headache that does not respond to analgesics
  • Unsteady gait
  • Gradual loss of consciousness
  • Increased nausea and vomiting
  • Retinal hemorrhage

Altitude sickness prevention

The body has an amazing ability to acclimatize to altitude, but it needs time. Ascending slowly is the best way to avoid altitude sickness. Avoiding strenuous activity such as skiing, hiking, etc. in the first 24 hours at high altitude reduces the symptoms of AMS.   AVOID alcohol and sleeping pills as they are respiratory depressants, and effectively slow down the acclimatization process and should be avoided. Alcohol also tends to cause dehydration and exacerbates AMS. Thus, avoiding alcohol consumption in the first 24–48 hours at a higher altitude is optimal.


Increased water intake may also help in acclimatization to replace the fluids lost through heavier breathing in the thin, dry air found at altitude, although consuming excessive quantities (“over-hydration”) has no benefits and may cause dangerous hyponatremia.


Can I take drugs to prevent altitude sickness?

As with everything, many ‘quack’ treatments and untested herbal remedies are claimed to prevent mountain sickness. These treatments can make AMS worse or have other dangerous side effects – many herbs are poisonous. Only one drug is currently known to prevent AMS and to be safe for this purpose: acetazolamide (diamox). The Centers for Disease Control and Prevention (CDC) suggest the same dose for prevention of 125 mg acetazolamide every 12 hours. Acetazolamide, a mild diuretic, works by acidifying the blood. This change in pH stimulates the respiratory center to increase the depth and frequency of respiration, thus speeding the natural acclimatization process. An undesirable side-effect of acetazolamide is a reduction in endurance performance. Other minor side effects include a tingle-sensation in hands and feet, and it can make carbonated drinks taste “flat”. Although a sulfonamide, acetazolamide is a non-antibiotic and has not been shown to cause life-threatening allergic cross-reactivity in those with a self-reported sulfa allergy.  This drug should only be taken at the direction of your primary care physician.


Prior to the onset of altitude sickness, ibuprofen is a non-steroidal anti-inflammatory that may help reduce the headache and nausea associated with AMS.

Author: Dr. Lindsey Nelson