Blowing is cold and breathing is hot, which is caused by different airflow speeds and different exhalation methods. When blowing, the opening area of the mouth is small, so the gas velocity is high. When the gas velocity is accelerated, the time for heat exchange with the skin surface is not enough, and the main function after contact with the skin is to accelerate evaporation. Evaporation is an endothermic process, which leads to a rapid drop in human body temperature. So when do people feel like blowing? Cold? Yes ? Huh? The opening area is large, the gas flow rate is relatively slow, and evaporation is not obvious. Exhaled gas meets human skin, and water vapor liquefies on the skin surface, releasing heat and being absorbed by the skin, so people feel hot.