Body / Life

Why do we get a fever?

The short answer

A fever is one of the body's responses to infection or illness. The brain temporarily raises the body's temperature setting, and the body works toward that new setting. This change can help the body's defenses and make it harder for some bacteria and viruses to grow.

A comparison: fever raises the brain's temperature setting, while heat from the surroundings or activity builds up in hyperthermia. — A high body temperature can come from different processes: a raised setting during fever or heat building up in hyperthermia.

Is fever a disease?

Infection is a common cause, but some medicines and inflammation (the body's response to injury or irritation) can also trigger a fever. Hyperthermia is different: heat from a hot place or strenuous activity builds up faster than the body can release it. Heat illness is caused by too much heat; its severe form, heatstroke, can affect how a person thinks or responds. Body temperature also changes with the time of day and where it is measured, so one reading cannot identify the cause. Learn how fever differs from hyperthermia, and why fever can cause chills, in “Why can a fever cause chills?”.

What should you do for a fever?

Rest, drink fluids, and watch for changes such as trouble breathing or difficulty drinking. The temperature number alone cannot show what caused the fever or how serious the illness is. Seek medical advice if a high fever lasts, breathing becomes difficult, or another worrying change appears.

What if someone seems confused after heat exposure?

After time in a hot place or strenuous exercise, confusion, a seizure, or unusual responses can be signs of severe heat illness. Call your local emergency number right away. While help is on the way, move the person to a cool place and loosen extra clothing. Pour cool water over the skin or place cool, wet cloths on it, and use a fan to help it cool. Give small sips of water only if the person is fully alert and can swallow. Do not give anything by mouth if they are confused, having a seizure, vomiting, or unable to swallow. Fever-reducing medicines do not treat heatstroke and may be harmful.

When should a young baby get medical advice?

An infant younger than 3 months with a rectal temperature of 38°C (100.4°F) or higher needs prompt medical advice, even if they seem well. If you use another method, follow local guidance on how to measure temperature and where to seek care. Medication and doses vary by age and health.

Sources

This article provides general information and is not a diagnosis or a substitute for medical care.