Wang K, et al. - Via conducting a two-stage, perspective observational study, researchers investigated physiological, hematological and biochemical risk factors associated with high-altitude headache (HAH) after acute exposure to 3700 m. They analyzed total 318 young Han Chinese males who ascended from sea level (altitude of 50 m) to altitude of 3700 m by train in 72 h. Higher heart rate (HR) and lower oxygen saturation (SpO₂) remained the independent risk factors for HAH. At both 50 m and 3700 m, lower blood urea nitrogen has emerged as a novel independent risk factor for HAH, providing new insights for understanding the pathological mechanisms.