Muscles
Associated with each hair follicle are smooth muscle cells, the arrector pili .
contracttion of the arrector pili causes the hair to become more perpendicular to the skin's surface, or to "stand on end ", and also produces a raised area of skin called "goose flesh."
In animals with fur, contraction of the arrector pili is beneficial because it increases the thickness of the fur by raising the hairs.
In the cold, the thicker layer of fur traps air and becomes a better insulator.
the thickened fur can also make the animal appear larger and more ferocious, which might deter an attacker.
It is unlikely that humans, their sparse amount ofhair, derive any important from contraction of their arrector pili.