High altitude pulmonary edema (HAPE) is a serious condition that can occur when individuals ascend to high altitudes, typically above 8,000 feet (2,400 meters). It is caused by a lack of oxygen, which leads to fluid accumulation in the lungs, making it difficult to breathe. Symptoms often include shortness of breath, cough, and fatigue. HAPE can develop within hours or days after reaching high altitudes. It is more common in those who ascend rapidly without proper acclimatization. Treatment involves descending to a lower altitude and may include supplemental oxygen or medications to reduce fluid in the lungs.