Humans need to regulate their internal body temperature to keep it constant because a rise in internal body temperature can lead to our organs overheating, fatigue, heat exhaustion and heat stroke. The body’s largest organ, the skin, is also designed to remove heat from the body. The most noticeable way is losing heat via evaporating sweat.
When the skin or core body temperature rises sufficiently, the thermostat in the brain sends impulses via our central nervous system to increase blood flow to the skin. The thermostat also activates the sweat glands. The sweat glands release droplets onto our skin that become vapour when the blood flowing through the skin passes underneath. As the sweat vaporizes, energy (in the form of heat) passes into the environment, cooling the blood. This cooled blood gets circulated back to the heart and brain, and cools the core body temperature.