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 against hypothermia, which can occur when exposed to extreme cold. In addition to cold, shivering can also be triggered by 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 initiating shivering when necessary. This process helps ensure that vital organs remain warm and function properly.