| What it is | Brain swelling at altitude |
| Symptoms | Confusion, ataxia, altered consciousness |
| Severity | Deadly emergency |
| Response | Immediate descent + emergency care |
HACE (high-altitude cerebral edema) is a rare but deadly form of altitude illness in which the brain swells with fluid, causing confusion, loss of coordination, and altered consciousness. It is a medical emergency requiring immediate descent and treatment; without rapid action, HACE can be fatal within hours.
Warning signs
Confusion, stumbling or inability to walk heel-to-toe (ataxia), severe headache, drowsiness, and behavioral change — usually following untreated AMS.
HACE vs HAPE
HACE hits the brain; HAPE hits the lungs — see HAPE vs HACE. Both mean descend now. Educational only; not a substitute for professional medical advice — seek emergency care.
Frequently asked questions
What is HACE?
HACE is high-altitude cerebral edema — swelling of the brain caused by altitude, usually as the end stage of severe altitude sickness. It impairs thinking and coordination and rapidly becomes life-threatening. It is one of the most serious mountain medical emergencies.
What are the symptoms of HACE?
The hallmark signs are confusion and a loss of coordination (ataxia) — for example being unable to walk a straight line — along with severe headache, drowsiness, behavioral changes, and progressing to unconsciousness. A classic field test is heel-to-toe walking.
What's the difference between HACE and HAPE?
Both are severe altitude illnesses, but HACE affects the brain (confusion, loss of coordination), while HAPE affects the lungs (breathlessness, cough). They can occur together. Both demand immediate descent and emergency care.
Sources
- High-altitude cerebral edema — Wilderness Medical Society
- Altitude illness — UIAA Medical Commission