A fever is a temporary increase in your body temperature, often due to an illness. Having a fever is a sign that something out of the ordinary is going on in your body.Fever or elevated body temperature might be caused by:A virus, a bacterial infection, heat exhaustion, or excessive work. In a healthy adult, a mild fever may be transient and the body is able to cope without any risk to the health of a person, in this case over the counter paracetamol is enough, However, high fevers (above 40 degrees Celsius/104 degrees Farenheit) or a persistent fever may be an indication of more serious underlying causes that need to be isolated and treated as soon as possible.