The inflammatory response is the body's defense against infection, injury, or irritation from bacteria, trauma, toxins, or heat. Inflammation helps locate and destroy pathogens and remove damaged tissue elements to heal the body. During this initial phase, fluid, blood products, and nutrients migrate to the injured area, resulting in redness, heat, swelling, ache, and loss of function. Moreover, signs of systemic inflammation include fever, increased WBC count, malaise, anorexia, nausea, vomiting, lymph node enlargement, or organ failure.

The crucial components of the inflammatory process are the vascular and cellular stages. At the vascular stage, small blood vessels constrict initially; then, the arterioles and venules that supply the area dilate, increasing the blood flow and causing redness and heat. In addition, the release of cell mediators, such as histamine, increases vascular permeability and allows protein-rich fluids to flow into the area, which can cause swelling, pain, and loss of function. During the cellular stage, white blood cells rush into the area. Neutrophils and monocytes engulf pathogens through phagocytosis and ingest cell debris and foreign material. This leads to the phagocytic release of pyrogens from bacterial cells, causing fever.