Condition

Fever

Fever means a rise in body temperature above normal (over 38 °C in adults). It is the body’s defence response, which hinders the growth of bacteria and viruses.

The most common causes are viral infections (common cold, COVID-19), bacterial infections (tonsillitis, pneumonia, urinary tract infection) or inflammatory diseases. Certain medicines and cancers can also cause fever.

Mild fever (below 38.5 °C) does not always need to be reduced, as it is part of the body’s defence response. High or prolonged fever requires a doctor’s assessment.

Source: Terveyskirjasto / Duodecim

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Practitioners – Fever

Frequently asked questions

When does fever require a doctor’s visit?

See a doctor if the fever is over 39.5 °C, lasts more than 3–5 days, is associated with a stiff neck, severe headache or rash, or if the person is clearly unwell. In children and older adults, even a lower fever warrants assessment more readily.

Does fever always need to be reduced with medicine?

Not necessarily. Moderate fever (38–38.5 °C) may speed recovery because it enhances the immune system’s function. Medicines (paracetamol, ibuprofen) are used if the fever causes significant discomfort or is very high. Staying hydrated is the most important thing.

Can vaccination cause fever?

Yes. A mild fever after vaccination is a normal sign of the immune response and shows that the vaccine is working. It usually lasts 1–2 days and can be eased with paracetamol if needed. A strong or prolonged fever reaction after vaccination is a reason to contact a doctor.

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