Why does our temperature go up when we are ill? Premium

Fever is the body's response to infection, triggered by cytokines that increase body temperature to fight pathogens.

A: The increase in core temperature observed during illness is commonly called fever and occurs in response to infection by a pathogen or certain types of physical injury. When a person becomes infected with bacteria, the white blood cells of the immune system recognise the incoming pathogen as foreign and initiate the first stages of the immune response: the acute phase.

In this reaction, white blood cells called monocytes release a variety of proteins called cytokines. They are central to the immune response. In particular, there is a predominance of two types of cytokine called interleukin-1 and tumour necrosis factor-alpha. These cytokines cause an increase in body temperature.

It is not clear how but it is known that they also cause the production of other chemicals in the brain. The main group of chemicals here are the postaglandins. They react very strongly with the hypothalamus area of the brain, which then sends a signal to the body to increase the temperature.

The mechanisms that the brain employs to effect this are not certain but are known to include increasing the metabolic rate and shivering. These two processes burn metabolic fuel faster than normal, and body heat is given off.

Experimental work shows that elevated temperatures can enhance certain aspects of the immune response. The growth rates of various types of bacteria are slowed at temperatures above normal body temperature.

- Nigel Eastmond, University of Liverpool