An antipyretic is a type of medication that will prevent or reduce fever by lowering body temperature from a raised state. They will not affect normal body temperature if the patient does not have a fever. Generally, most non-steroidal anti-inflammatory drugs (NSAIDs) work by inhibiting prostaglandin synthetase within the hypothalamus. Fever, or pyrexia, occurs when the body reaches a temperature above what is considered "average". Bear in mind, however, that this "average" temperature can vary from person to person within certain parameters. It is generally accepted fever exists at a temperature above 37 degrees Celsius (98.6 degrees Fahrenheit) when the thermometer is placed under the armpit, or over 37.5 degrees Celsius (99.5 degrees Fahrenheit) when measured orally or rectally.Fever usually results from microbes such as bacteria or viruses triggering the body's defence mechanisms. This activates certain types of cells, some of which release the substance interleukin. Prostaglandin is another chemical released by the body that plays a part in this process. Prostaglandin is induced by bacterial pyrogens and is produced in the Central Nervous System (CNS). Interleukin affects the hypothalamus, which is the part of the brain that regulates body temperature, signalling it to raise the temperature by a few degrees. The hypothalamus works like a thermostat while the interleukin that is released serves to raise its preset temperature.The body has a number of techniques that it uses to achieve this change in temperature. Shivering involves physical movement that produces heat. Vasoconstriction, which entails the constriction of blood flow beneath the skin, reduces the amount of heat lost from the body. It also causes one to feel cold in their extremities, such as the hands and feet, prompting them to be covered up.How is this increase in temperature part of the body's defence mechanism? The body raises the temperature in an effort to create an inhospitable environment for the microbes that cause the infection. Fever is a symptom of illness is part of the body's attempts to rid itself of the infection and inhibit its spread. Once the infection has been dealt with, the fever is said to have "broken" and the patient feels overheated, breaking out in a sweat as the body tries to cool down to its normal temperature. Vasodilatation of peripheral blood vessels also occurs at this stage, increasing the blood flow once again.Antipyretics work by getting the "thermostat" in the hypothalamus to override the interleukin-induced increase in temperature. The body will then work to lower the temperature to the new, lower temperature and the result is a reduction in the fever. Antipyretics will also reduce prostaglandin synthesis in the hypothalamus by inhibiting the effect of endogenous or microbial pyrogens on the heat regulating sensors of the hypothalamus. By blocking prostaglandin synthetase, antipyretics prevent a rise in prostaglandin levels in the brain.