The human body has a normal temperature of 36 to 37 degrees Celsius. It therefore stands to reason that the ideal outside temperature for humans is the same as their body temperature. However, we find 36 degrees outside too hot and feel most comfortable at 20 to 25 degrees. Why is that?

If you place a bowl of hot water in an environment that is colder than the water, the water gradually cools down and adapts to the outside temperature. A balance is created between the two temperatures. Heat naturally flows to cooler areas.
Unlike the bowl of water, the human body is constantly generating new heat, so it does not adapt to the outside temperature. If this heat were to build up, which happens at temperatures of more than 30 degrees, if we do not cool down, the body would overheat. In other words, the heat has to escape from the body. The greater the temperature difference between the body and the environment, the faster the heat escapes.

An outside temperature of between 20 and 25 degrees is therefore the most comfortable for the human body, because body heat escapes from the body just as quickly as it is generated.