Blood vessels near the surface of the skin constrict to prevent heat loss to the environment and maintain blood flow around the central organs. This is called vasoconstriction. Also, skeletal muscles contract and relax rapidly causing shivering, which raises the body temperature. Another response to cold temperatures is erector muscles contracting causing hairs to stand on end, which traps an insulating layer of air. Sweat production is reduced and this also prevents heat loss to the environment.