Warming us up
When our skin is cold our skin acts to reduce heat loss.
The hair erector muscles contract and make the hairs stand more upright.
This traps warm still air close to the skins surface.
Less heat is lost by radiation.
Sweat glands stop producing sweat.
Blood vessels near the skins surface get narrower so less blood gets near the surface.
This reduces heat loss by radiation.
Cooling us down
When our skin is hot our skin acts to increase heat loss.
The hair erector muscles relax and make the hairs lie flat against the skin.
Less air is trapped close to the skins surface.
More heat is lost by radiation.
Sweat glands start producing sweat which evaporates off the skins surface using heat energy from the skin thus cooling us down.
Blood vessels near the skins surface widen so more blood gets near to the surface.
This increases heat loss by radiation.