Fever
Fever is a common symptom of an anti-infection defense mechanism.
Wikipedia / Wikimedia Commons
Fever, also known as pyrexia in humans, is a symptom of an anti-infection defense mechanism that appears when body temperature exceeds the normal range, caused by an increase in the body's temperature set point in the hypothalamus. It is one of the most common medical signs, occurring in about 30% of healthcare visits by children and up to 75% of seriously sick adults. Fever evolved as a defense mechanism, though treating it does not appear to improve or worsen outcomes.
- field
- Medicine
- known_for
- Common medical sign of elevated body temperature due to increased hypothalamic set point
- associated_symptoms
- Lethargy, depression, loss of appetite, sleepiness, hyperalgesia, dehydration, inability to concentrate, fever dreams, mild to severe delirium
- causes
- Viral, bacterial, and parasitic infections; non-infectious causes include vasculitis, deep vein thrombosis, connective tissue disease, medication side effects, vaccination, and cancer
- treatment
- Generally not required; ibuprofen or paracetamol may help with pain and inflammation; hyperthermia requires treatment
Lore & Background
Fever is triggered by pyrogens, which cause the release of prostaglandin E2 (PGE2) in the hypothalamus, raising the body's temperature set point. The hypothalamus then orchestrates heat production through increased muscle tone, shivering, and hormone release, as well as heat conservation via vasoconstriction. When the set point returns to normal, sweating and vasodilation cool the body. Fever rarely exceeds 41 to 42 °C (106 to 108 °F) and may trigger febrile seizures, more common in young children.
Reader's Guide
Fever is a significant medical sign, part of about 30% of pediatric healthcare visits and up to 75% of serious adult illnesses. It is often viewed with greater concern by parents and healthcare professionals than warranted, a phenomenon known as 'fever phobia.' While fever evolved as a defense mechanism, treating it does not appear to improve or worsen outcomes. Distinguishing fever from hyperthermia is clinically important, as hyperthermia can quickly lead to death and does not respond to antipyretic medications. Fever is caused by a wide range of conditions, from non-serious to life-threatening, including infections and non-infectious causes such as cancer and medication side effects.
Did You Know?
- There is no single agreed-upon upper limit for normal temperature; sources use values between 37.2 and 38.3 °C (99.0 and 100.9 °F).
- Fever is part of about 30% of healthcare visits by children and occurs in up to 75% of adults who are seriously sick.
- Fever differs from hyperthermia, which is an increase in body temperature over the set point due to too much heat production or not enough heat loss.
- Sleeping with a fever can often cause intense or confusing nightmares, commonly called 'fever dreams.'
Frequently Asked Questions
Who is Fever?
Fever is the body's built-in anti-infection response that activates when the hypothalamus pushes the internal temperature set point above the normal range. It manifests as an elevated body temperature and stands as one of the most frequently observed medical signs in clinical practice.
What triggers Fever?
The most common triggers are viral, bacterial, and parasitic infections, though non-infectious factors such as certain medications, vaccinations, vasculitis, deep vein thrombosis, connective tissue disorders, and cancer can also set it off.
What sensations come alongside Fever?
The typical companion cluster includes lethargy, loss of appetite, sleepiness, heightened pain sensitivity, dehydration, and difficulty concentrating. In more severe presentations, fever dreams and mild-to-severe delirium may also appear.
How is Fever treated?
In most cases no intervention is needed, and evidence suggests that suppressing it neither improves nor worsens the underlying outcome. When relief is desired, ibuprofen or paracetamol can ease pain and inflammation, but true hyperthermia does require active medical treatment.
Why is Fever important in the canon?
Fever evolved specifically as a defense mechanism against infection, making it a cornerstone of the body's immune response. It shows up in roughly 30% of pediatric healthcare visits and up to 75% of seriously ill adult cases, cementing its status as one of the most common signs in all of medicine.
More in Symptoms And Sensations 1-18
Spotted an error? Know more?
This is a living reference — every entry is fact-audited, and reader corrections feed straight into our audit queue. Suggest an edit · See this site's audit record