Fever: what it is for, and when it means something else

Fever is a regulated rise in body temperature in response to infection. It is a symptom of an immune response rather than a disease in itself, and the reason to treat it is comfort, not the number.

What the evidence supports. Antipyretics — paracetamol or ibuprofen at a weight-based dose — make a febrile person more comfortable and do not treat the underlying illness. Routine aggressive fever reduction has not been shown to improve outcomes in most infections; treating a comfortable person's fever for its own sake is not required. Fluids matter more than the temperature. And for a child, the number matters far less than how the child looks and behaves.

Do not use aspirin in a child or teenager with a fever or a viral illness, because of Reye's syndrome. Do not alternate paracetamol and ibuprofen to "chase the fever" without a clear plan, because dosing errors are common.

Physical measures. Tepid sponging and fans make the person comfortable; do not use cold water or ice, do not use alcohol rubs (which are absorbed and toxic), and do not bundle a febrile person up to "sweat it out" — that is how heat illness develops.

Dehydration is the real risk in a febrile illness, and the treatment is oral rehydration solution in the correct proportions: 1 litre of water, 6 level teaspoons of sugar, half a level teaspoon of salt. Not plain water alone, not a sports drink, and do not add extra sugar.

Fever in specific situations needs care:

• Under 3 months: any fever above 100.4 F / 38 C is an emergency and needs immediate assessment, because infants cannot localise infection and can look deceptively well.
• A fever with a stiff neck, a rash that does not fade under pressure, confusion, or severe headache — emergency care, possible meningitis.
• A fever with breathlessness, flank pain, or a red hot swollen area — assessment.
• A fever after travel abroad, or in a person who is immunosuppressed or on chemotherapy — urgent assessment, because the ordinary causes do not apply.
• A fever that returns after improving, or that lasts more than 5 days — assessment.
• A fever with a very high temperature and no sweating, hot dry skin, confusion or collapse — heat stroke, emergency care. Do not confuse this with ordinary fever.

The fever that is not an infection. Fever can be a drug reaction, an inflammatory disease, a malignancy, or a thyroid problem. A fever with no obvious source, recurring, or with night sweats and weight loss needs assessment.