Animation showing vasodilation in skin

During vasodilation, the capillaries near the surface your skin dilate (widen) to carry more blood to the surface of your skin so you can lose heat from your body. The sweat glands in the skin release sweat, which evaporates from your skin taking heat away. Hair on your body lies flat and can help sweat evaporate off your body.

During vasoconstriction, the capillaries closer to the surface of the skin constrict (get narrower) so there is less blood flowing to the surface. Shivering makes the skin shake. Hairs in the skin stand on end to trap a layer of air next to the skin so less heat is lost due to conduction.