Sweat glands and fatty layers in the skin help to regulate body temperature in mammals. When the outside temperature is high, sweat glands release bodily fluids combined with salt to keep the body temperature from getting too high. When the outside temperature is low, fatty layers on the skin act as insulation, trapping heat and keeping it from leaving the body.
Temperature receptors are located within the skin. These receptors send signals to the body, stimulating shaking in cold weather and sweating in hot weather. When the temperature outside is high, sweat glands within the skin react. The human body has roughly 2.6 million sweat glands. When the body senses an increase in the core temperature, it responds by increasing blood flow to the skin, which stimulates the sweat glands. They begin to release a fluid mixed with salt known as perspiration. When this perspiration releases from the pores, it settles on the outside of the skin. The effect of this perspiration and the outside wind help to cool the body off, lowering the internal temperature of the body. Fatty layers on the skin help the body to retain all the heat that it can during extremely low temperatures. Blood flow is directed further away from the skin to conserve warmth. During exercise, the body's ability to regulate heat, or thermoregulate, is challenged.