The human body has automatic responses to help regulate temperature. When the external environment heats up, arterioles leading to the capillary loops in the dermis dilate (widen). This increases blood flow to the surface of the skin where its heat can more easily radiate away. This process is called vasodilation. Sweat glands also produce greater amounts of sweat. This liquid is secreted onto the surface of the skin. Sweat needs energy to turn from a liquid into a gas and evaporate. This energy is called the latent heat of vaporisation. The body supplies this heat and so it cools down as the sweat evaporates.