At the root of each of the hairs distributed over the entire surface of the skin (except for the areas of the genitals, the palms of the hands and the soles of the feet) there is an erector hair muscle . When it is cold, this muscle contracts to bristle the hair, thus striving to create a layer of air around us that insulates us from the cold outside. It is what we know as "goose bumps" (or "goose bumps") . Blood vessels also contract to prevent loss of body heat.
This same reaction occurs when we feel fear due to the action of the sympathetic nerves.
