Chills

Chills are a feeling of coldness, usually accompanied by shivering, that typically occurs during a high fever but can also happen alone. They arise when inflammatory signaling molecules, cytokines and prostaglandins, raise the body's internal temperature set point in the hypothalamus; because the body has not yet caught up to this new higher target, the person feels cold and shivers, generating heat through vasoconstriction and muscle activity, until body temperature reaches the new set point and the chills stop. Severe chills with violent shivering are called rigors, while isolated chills without a fever are usually mild and can even be triggered briefly by sudden fright. Once the underlying trigger passes, the set point falls again, producing what is sometimes called a crisis phase of sweating and skin flushing as the body sheds the excess heat.