AltitudeAheadUnderstanding altitude sickness
Acute mountain sickness, HACE and HAPE: what they are and why severe symptoms need urgent action.
Why altitude affects you
As you go higher, air pressure falls and each breath carries less oxygen. Your body can adapt, but it needs time. When you ascend faster than you adapt, altitude illness can develop.
Altitude illness can occur from about 2,500 m, and sometimes lower. It can affect anyone — fitness, age and previous trips without problems don't reliably protect you.
Acute mountain sickness (AMS)
AMS is the most common form. The main symptom is headache, typically with one or more of: tiredness or weakness, loss of appetite or nausea, and dizziness or light-headedness. It usually starts within hours to a day after arriving at a new, higher altitude.
AMS feels a lot like a hangover or a viral illness. At altitude, assume these symptoms are altitude illness until proven otherwise.
High-altitude cerebral edema (HACE)
HACE is swelling of the brain and is life-threatening. It usually develops from worsening AMS. Warning signs are loss of coordination (stumbling, unable to walk a straight line), confusion, unusual behavior or drowsiness.
Someone with signs of HACE needs to descend immediately with company and get medical help.
High-altitude pulmonary edema (HAPE)
HAPE is fluid in the lungs and is life-threatening. It can occur with or without AMS. Early signs are unusual breathlessness on exertion and reduced performance, then breathlessness at rest, cough, chest tightness, and sometimes frothy or blood-stained sputum.
Someone with signs of HAPE needs to descend and get medical help urgently. Exertion makes HAPE worse, so they may need to be helped down.
What increases risk
The main factors are how high you sleep, how fast you gain sleeping altitude, and individual susceptibility — especially a previous episode of altitude illness. Arriving directly at high altitude, for example by plane, also adds risk.
AltitudeAhead can check your itinerary against general ascent recommendations, but it can't see your health, your history or how you feel on the day.
General information, not medical advice. If you have symptoms at altitude, don't go higher. See the medical disclaimer.
