Fever (also known as pyrexia or a febrile response) is defined as a body temperature above the normal range due to an increase in the temperature regulatory set-point. There is not a single agreed upon upper limit for normal temperature with sources using values between 37.5 and 38.3 °C (99.5 and 100.9 °F). The increase in set-point triggers increased muscle tone and causes a feeling of cold resulting in greater heat production and efforts to conserve heat. This results in an increase in body temperature. When the set-point temperature returns to normal a person feels hot and may begin to sweat.A fever can be caused by many medical conditions ranging from the not serious to potentially serious. This includes viral, bacterial and parasitic infections such as the common cold, urinary tract infections, meningitis, malaria and appendicitis among others. Non infectious causes include vasculitis, deep vein thrombosis, side effects of medication, and cancer among others.A fever may be useful as a defense mechanism as the body's immune response can be strengthened at higher temperatures; however, there are arguments for and against the usefulness of fever, and the issue is controversial. With the exception of very high temperatures, treatment to reduce fever is often not necessary. Antipyretic medications such as ibuprofen or paracetamol can be effective at lowering the temperature, which may improve comfort.Fever is one of the most common medical signs. It differs from hyperthermia, in that hyperthermia is an increase in body temperature over the body's thermoregulatory set-point, due to excessive heat production or insufficient heat loss.