How does skin sense heat leaving the body?

When heat leaves the body, specialized nerve endings in the skin—called thermoreceptors—detect this change in temperature. These receptors, which are found in both the epidermis and dermis, monitor the skin’s temperature by directly sensing the energy balance that results when heat is lost via conduction, convection, or radiation^[8][5]

As heat exits the skin, its temperature drops. This cooling causes a change in the cell membrane of thermoreceptors; in particular, temperature-sensitive proteins such as transient receptor potential (TRP) channels respond by altering their ion flow. For instance, some TRP channels are tuned to activate when the skin cools, converting the thermal loss into electrical signals (graded potentials that lead to action potentials) which then travel along nerve fibers to the brain^[8][5]

These electrical signals inform the nervous system about changes in skin temperature. When heat is being lost, cold receptors typically increase their firing rate, alerting the brain that the local temperature has dropped. This information is used not just for the perception of the environment but also to help trigger protective thermoregulatory responses—such as reducing blood flow to the skin (vasoconstriction) or initiating shivering—to conserve body heat^[9][14]

Furthermore, the materials that come in contact with the skin can affect this process. For example, a metal object may feel cooler than a plastic one even at the same temperature because metal conducts heat away from the skin more efficiently, thereby accelerating the rate at which heat is lost and enhancing the cooling sensation^[8][13]