Shivering is an involuntary response of the body to cold temperatures. It occurs when muscles rapidly contract and relax, generating heat to help maintain body temperature. This reaction is part of the body's natural defense mechanism to prevent hypothermia, a condition that can occur when the body loses heat faster than it can produce it. In addition to cold exposure, shivering can also happen during fever as the body tries to raise its temperature to fight off infection. The brain's hypothalamus plays a key role in regulating body temperature and triggering shivering when needed.