Fever activators are substances that activate the body’s endogenous pyrogen-producing cells to produce and release endogenous pyrogens, which then cause an increase in body temperature through subsequent remission. Fever activators can be classified into the following four categories: 1. exotoxins; 2. endotoxins; 3. necrotic tissue disintegrants; and 4. antigen-antibody complexes. The common ones are microorganisms, including endotoxins of gram-negative bacteria, exotoxins of gram-positive bacteria, viral infection spirochetes, inflammatory agents, antigen-antibody complexes, lymphokines, and steroids. Traumatic pyrogens act on the skin and visceral vessels to activate endogenous pyrogenic cells that produce and release endogenous pyrogens, which in turn act on the thermoregulatory centers to cause fever.