The arrector pili is a |smooth muscle| of the skin. It is attached to a |hair follicle| just below its oil gland and extends upward on a slant to attach to the skin. The muscle reacts in response to cold or other stimuli. When it contracts, the muscle pulls the hair erect causing "goose bumps". At the same time, it squeezes the oil gland releasing a small amount of oil onto the skin.
