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Why does an inflamed area feel warm?
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inflammation
The main function of complement proteins is to aid in the destruction of pathogens by piercing their outer membranes (cell lysis) or by making them more attractive to phagocytic cells such as macrophages (a process known as opsonization). Some complement components also promote inflammation by stimulating cells to release histamine and by attracting phagocytic cells to the site of infection.
An inflamed area feels warm primarily due to increased blood flow to the site of injury. Following an initial, brief period of vasoconstriction, the small blood vessels in the affected area undergo vasodilation, which significantly increases the volume of blood circulating through the tissue. This sensation of heat is typically experienced in peripheral parts of the body, such as the skin.123
Additionally, chemical mediators released during the inflammatory process can contribute to a localized rise in temperature at the site of injury. This heat is one of the four cardinal signs of inflammation, a classification first described by the Roman medical writer Aulus Cornelius Celsus in the 1st century CE.12