Fever
Fever is an elevated body temperature due to a raised hypothalamic set point.
Wikipedia / Wikimedia Commons
Fever, also known as pyrexia, is a common medical sign in humans characterized by an elevation of body temperature above the normal range due to an increase in the body's temperature set point in the hypothalamus. It is a symptom of an anti-infection defense mechanism and is one of the most frequent reasons for healthcare visits, occurring in about 30% of children's visits and up to 75% of seriously ill adults.
Quick Facts
- Field
- Internal medicine, pediatrics
- Symptoms
- Initially: shivering, feeling cold, chills / Later: flushed, sweating
- Complications
- Febrile seizure, disseminated intravascular coagulation, brain injury
- Causes
- Virus, bacteria, increase in the body's temperature set point
- Diagnosis
- Temperature higher than the normal range of 37.2 and
- Differential
- Hyperthermia
- Treatment
- Based on underlying cause, not required for fever itself
- Medication
- Antipyretics (ibuprofen, paracetamol)
- Frequency
- Common
Facts from the source article.
Lore & Background
Fever is triggered by pyrogens, which can be either endogenous (cytokines like interleukin 1 and interleukin 6 released from immune cells) or exogenous (such as bacterial lipopolysaccharides). These pyrogens cause the release of prostaglandin E2 (PGE2) in the hypothalamus, which raises the body's temperature set point. The body then increases heat production through shivering and muscle contractions, and conserves heat via vasoconstriction, leading to a feeling of cold or chills. When the set point returns to normal, the person feels hot, becomes flushed, and may sweat.
Reader's Guide
Fever is a significant medical sign that has evolved as a defense mechanism against infection, though treating it does not appear to improve or worsen outcomes. It is often viewed with greater concern by parents and healthcare professionals than is usually deserved, a phenomenon known as 'fever phobia'. Fever can be caused by a wide range of conditions, from non-serious viral infections to life-threatening diseases such as meningitis, appendicitis, and cancer. It is distinct from hyperthermia, which is an elevation of body temperature over the set point due to excessive heat production or inadequate heat loss, and which requires different treatment. While fever itself generally does not require treatment, medications like ibuprofen or paracetamol may be used to address associated pain and inflammation. Children younger than three months and people with serious medical problems or compromised immune systems require medical attention.
Did You Know?
- Fever is part of about 30% of healthcare visits by children and occurs in up to 75% of adults who are seriously sick.
- Rarely, a fever may trigger a febrile seizure, which is more common in young children.
- Fever differs from hyperthermia, in which body temperature rises above the set point due to too much heat production or not enough heat loss.
- The hypothalamus can be seen as working like a thermostat, with the EP3 subtype of PGE2 receptor mediating the fever response.
Frequently Asked Questions
Who is Fever?
Fever is the body's internal alarm that activates when the hypothalamus resets the thermal thermostat to a higher number, pushing core temperature above the usual baseline. It is one of the most frequently encountered signs in clinical medicine, appearing in roughly a third of pediatric visits and as many as three-quarters of cases among seriously ill adults.
What are Fever's powers or role?
Its primary function is to act as an anti-infection shield, making the internal environment less hospitable to invading pathogens while simultaneously boosting immune-cell activity. It is essentially the body's built-in defense protocol rather than a disease in its own right.
What triggers Fever to show up?
Chemical messengers called pyrogens—released by immune cells or directly by microbes—signal the hypothalamus to raise the body's target temperature. Once that set point shifts upward, the body generates and retains heat until the underlying trigger is resolved.
What are Fever's typical limits and side effects?
There is no single universally agreed-upon cutoff, with different references placing the threshold anywhere from about 37.2 °C to 38.3 °C, and extreme cases can push toward 41–42 °C. Alongside the heat, it drags in a cluster of sickness-behavior effects such as fatigue, poor appetite, sleepiness, heightened pain sensitivity, and in severe cases, confusion or delirium.
How do people treat or dismiss Fever?
The go-to approach is antipyretic medications such as ibuprofen or paracetamol, which work by nudging the hypothalamic set point back down. In most mild cases it resolves on its own once the underlying infection clears, but persistent or very high readings warrant a medical evaluation.
More in Symptoms and signs 1-24
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