Chills

Chills is a feeling of coldness occurring during a high fever, but sometimes is also a common symptom which occurs alone in specific people. It occurs during fever due to the release of cytokines and prostaglandins as part of the inflammatory response, which increases the set point for body temperature in the hypothalamus. The increased set point causes the body temperature to rise (pyrexia), but also makes the patient feel cold or chills until the new set point is reached. Shivering also occurs along with chills because the patient's body produces heat during muscle contraction in a physiological attempt to increase body temperature to the new set point. When it does not accompany a high fever, it is normally a light chill.

Sometimes a chill of medium power and short duration may occur during a scare, especially in scares of fear, commonly interpreted like or confused by trembling.

Severe chills with violent shivering are called rigors.

Pathophysiology
Chills occur when the hypothalamic temperature set point is suddenly elevated. This could occur due to several causes, including tissue destruction, pyrogenic substances, or dehydration. Due to the body temperature being below the new set point, body mechanisms of raising body temperature, including vasoconstriction, and shivering ensue. The person experiences this period as extreme cold, even though they might have an elevated body temperature than normal. As the body temperature rises and reaches the new set point, chills stop and the person feels neither hot nor cold. If the factor causing the high temperature is then removed, the hypothalamic set point decreases, but the body temperature is still higher than it. This then triggers the body cooling mechanisms to reduce the body temperature to the new set point, and is experienced as severe sweating, and hot skin due to vasodilation. This phase of the febrile state is known as the "crisis", or the "flush".

Causes
Chills are commonly caused by inflammatory diseases, such as influenza. Malaria is one of the common reasons for chills and rigors. In malaria, the parasites enter the liver, grow there and then attack the red blood cells which causes rupture of these cells and release of a toxic substance hemozoin which causes chills recurring every 3 to 4 days. Sometimes they happen in specific people almost all the time, in a slight power, or it less commonly happens in a generally healthy person.