In biochemistry, eicosanoids (preferred IUPAC name icosanoids) are signaling molecules made by oxidation of 20-carbon fatty acids. They exert complex control over many bodily systems; mainly in growth during and after physical activity, inflammation or immunity after the intake of toxic compounds and pathogens, and as messengers in the central nervous system. Many are classified as hormones. The networks of controls that depend upon eicosanoids are among the most complex in the human body.