When a person experiences strong emotions such as fear, nostalgia, pleasure, awe, admiration and sexual arousal or in cold, the stimulus causes the tiny muscles attached to each hair follicle known as arrectores pilorum, to contract This contraction causes the hair strands to literally "stand on end." At the same time, the tiny muscles that are contracting are causing a "bunching" of the skin surrounding the hairs, which results in the "bumps" commonly known as goosebumps and medically termed as cutis anserina.
Goose bumps are created when The reflex is started by the sympathetic nervous system. iT can be experienced in the presence of cold temperatures. This is the body's way of preserving its own heat by causing the hairs on the skin to stand up, thus reducing heat loss.