The term fever is used to refer to high core body temperature which may occur when the body is defending itself against pathogens such as viruses, bacteria or moulds.

Body temperature may fluctuate a little throughout the day but is normally between 36.0 and 37.4 degrees Celsius. Fever is also subdivided as follows:

• A temperature from 37.5 to 38 degrees Celsius is referred to as an elevated body temperature. 
• A temperature of 38 degrees Celsius or more is referred to by the medical term “fever”. 
  • Initially, however, temperatures up to 38.5 degrees Celsius are referred to as mild fever. 
  • Initially, however, temperatures up to 38.5 degrees Celsius are referred to as mild fever. 
  • Temperatures above 40 degrees Celsius are considered to be a very high fever.
  • In rare cases the core body temperature may increase above 41 degrees Celsius, in which case it is referred to as an extreme fever. 

There are normally three stages of a fever: the ascent phase, the peak and the decrease. In the ascent phase attempts are made to increase body temperature by goosebumps or trembling, which can cause shivering. In extreme cases fever-induced delirium may occur at the peak, when the fever is fully developed, with dimming of consciousness (obtundation) and perception. These clear as the body temperature falls and do not normally cause lasting damage. During the decrease phase when the temperature is falling, severe sweating may occur.

Those affected may experience severe headaches and aching limbs as well as pronounced discomfort during the fever. Drugs such as antipyretics (fever-reducing drugs) are available to reduce fever or mitigate these concomitant symptoms.