What part of the body is responsible for 50% of heat loss through radiation?

The head and neck are responsible for approximately 50% of heat loss through radiation due to their significant surface area relative to the volume of blood vessels that can transfer heat. The skin in these regions has a high density of blood vessels, enabling effective heat exchange with the environment. When the body is in a state of thermal regulation, heat is lost predominantly through radiation, which is the process of heat transfer in the form of infrared radiation from the warm surfaces of the body to cooler surrounding areas.

In contrast, while the torso, arms, and legs do participate in heat loss, they do not contribute nearly as significantly as the head and neck. The torso can retain a significant amount of body heat due to its encapsulation of vital organs, and while the arms and legs have some contribution, their surface area and vascularization do not match the head and neck's effectiveness in radiating heat. Thus, the head and neck primarily lead this process, making them the major area responsible for heat loss through radiation.