What your body is doing during a fever

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Exercising in the Heat
Fever and heatstroke both mean a high temperature, but the mechanisms differ: in a fever the set point is raised; in heatstroke heat production outruns heat loss, core temperature climbs above the set point, and temperature regulation fails. Heatstroke is an emergency that needs the body cooled right away.

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The thermostat gets turned up

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A fever is not body temperature running out of control. It is the brain deliberately raising its temperature target. That target is called the set point, and it is managed by a small area at the front of the hypothalamus called the preoptic area.

During an infection, innate immunity raises the first alarm: immune cells release a group of signalling molecules that cause fever, called pyrogens. They travel in the blood to the brain and act on the lining of its blood vessels, whose cells then make prostaglandin E2 (PGE2) on the spot. PGE2 acts on the preoptic area and releases its brake on the heat-making circuits; the body starts holding in heat and making more of it, and temperature is pushed toward the new, higher target.

Normal body temperature is not a fixed 37.0°C either. It is a range that shifts with where it is measured and with age.

The American Academy of Pediatrics stresses that fever is not an illness in itself but a physiological mechanism the body uses against infection. A baby under 3 months with a fever, or a child who cannot be woken or whose seizure will not stop, needs medical care right away.

Educational content, not medical advice. See a clinician about your own case.

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What your body is doing during a fever

Story

Connected to · 1

contrast · 1

Exercising in the Heat
Fever and heatstroke both mean a high temperature, but the mechanisms differ: in a fever the set point is raised; in heatstroke heat production outruns heat loss, core temperature climbs above the set point, and temperature regulation fails. Heatstroke is an emergency that needs the body cooled right away.

Read full story

Stop 1/5

The thermostat gets turned up

EVIDENCEGUIDE 1 · REVIEW 4

READ THE ORIGINAL

A fever is not body temperature running out of control. It is the brain deliberately raising its temperature target. That target is called the set point, and it is managed by a small area at the front of the hypothalamus called the preoptic area.

During an infection, innate immunity raises the first alarm: immune cells release a group of signalling molecules that cause fever, called pyrogens. They travel in the blood to the brain and act on the lining of its blood vessels, whose cells then make prostaglandin E2 (PGE2) on the spot. PGE2 acts on the preoptic area and releases its brake on the heat-making circuits; the body starts holding in heat and making more of it, and temperature is pushed toward the new, higher target.

Normal body temperature is not a fixed 37.0°C either. It is a range that shifts with where it is measured and with age.

The American Academy of Pediatrics stresses that fever is not an illness in itself but a physiological mechanism the body uses against infection. A baby under 3 months with a fever, or a child who cannot be woken or whose seizure will not stop, needs medical care right away.

Educational content, not medical advice. See a clinician about your own case.