Fever is typically an immune response stimulated by the release of certain chemicals (such as cytokines) in response to either an infection, autoimmune disorder, malignancy, or other causes. Persistent fever that does not improve or persists for more than 3–5 days should warrant an evaluation by a medical professional. Fever is a common sign, but it is not normal to have fever persistently, especially if there is no apparent clinical illness associated with the fever.