Why cant humans survive in the stratosphere?

Humans cannot survive in the stratosphere due to the lack of breathable oxygen and extreme atmospheric conditions. The stratosphere, which extends from about 10 to 50 kilometers above the Earth's surface, has significantly lower air pressure, resulting in insufficient oxygen for respiration. Additionally, temperatures can be very low, and exposure to increased levels of ultraviolet radiation can cause severe harm. Without specialized equipment, such as pressurized suits or breathing apparatus, humans cannot withstand these harsh environments.