Normal body temperature is 98.6°F (37.2°C). Fever is defined as a higher-than-normal body temperature. Certain pathogens and bacterial toxins may stimulate the release of pyrogens (proteins that regulate body temperature) such as interleukin-1. Increases in body temperature increase the metabolic rate and may speed up body reactions that aid to resolve infections. Fever may also inhibit the growth of certain microbes. Fever appears to stimulate the liver to hoard substances that bacteria require, helping to decrease bacterial growth.