Every person's temperature varies slightly, but the average "normal" temperature for humans is 37°C (98.6°F). Various things influence body temperature, for example activity, metabolic rate, environmental temperature, and infection.
Infection will cause an elevated temperature which is sometimes the only outside evidence of an infection, but other times is associated with obvious symptoms to suggest the cause. There is evidence that the body deals better with infection as a result of creating an elevated temperature. At the same time the body's immune system comes into action with special proteins being produced and mobilisation of white blood cells.
The raised temperature may be associated with shivering and hot sweats in turn. Shivering is the body's way of elevating the temperature and is brought about by the temperature regulating centre in the brain (the hypothalamus). Sweating performs the reverse function, once again regulated by the hypothalamus. When you have a fever it is as though the body has temporarily reset its thermostat.
Fever is also associated with headache, other bodily aches and pains, rapid breathing and rapid heart rate. In the presence of such symptoms people often prefer to take some treatment to alleviate them, but if the fever is only mild (eg only one degree above normal), and the symptoms not too severe, there is no need to take medication just to return the temperature to normal.
If the fever becomes very high (eg 39°C or 102.2°F plus) you should contact your doctor. Such high temperatures will sometimes bring with them clouded consciousness and hallucinations. In some children below the age of five, fever may lead to convulsions which are known as febrile convulsions.
Keep the patient well hydrated, ie give plenty to drink.
The most effective drugs to reduce temperature (anti-pyretics) are aspirin and other anti-inflammatory pain killers (NSAIDs) such as ibuprofen. These are ideal for use in adults as long as they are not usually adversely affected by them, and should not usually be given on an empty stomach. Aspirin should not be given to children under 16.
Paracetamol is a good second choice in adults who are not able to take the above, and probably the best option for children.
When the above drugs cannot be used, or are ineffective, sparse clothing and sponging with tepid water (at normal body temperature) helps to bring down the temperature. This mimics sweating, the body's natural cooling mechanism. (Paradoxically, cold water closes up the surface blood vessels of the skin causing the body temperature to stay the same or even rise.)
Usually the above measures help while the body's natural curing mechanisms take place or any other more active treatment of the underlying cause has its effect. If the temperature remains very high or other symptoms, eg state of consciousness affected or fits occur, contact a doctor. Equally fever can be a symptom of many other conditions and if in doubt about the other associated symptoms speak to a doctor.