A fever signals a temporary increase in your body’s core temperature. This elevation is not an illness, but a symptom, often indicating your immune system is actively combating an infection or inflammation. The human body maintains a stable internal temperature, usually around 98.6 degrees Fahrenheit (37 degrees Celsius). When this temperature rises, it suggests a biological response aimed at creating a less hospitable environment for invading pathogens.
The Body’s Fever Response
Fever initiation begins when the body encounters pyrogens. These can be external (like bacteria or viruses) or internal (produced by immune cells in response to infection). Pyrogens travel through the bloodstream to the hypothalamus, the body’s thermostat. The hypothalamus then resets the body’s temperature set point to a higher level.
To reach this elevated set point, the body initiates heat-generating and heat-conserving mechanisms. Muscles contract rapidly, causing shivering or chills, which produce heat. Blood vessels near the skin’s surface constrict (vasoconstriction), reducing blood flow and minimizing heat loss. These adjustments continue until body temperature aligns with the hypothalamus’s new set point, establishing the fever.
The Fever’s Resolution
A fever subsides when the underlying infection or inflammation resolves. As the immune system overcomes the threat, pyrogen production by immune cells decreases. This signals the hypothalamus that the elevated temperature is no longer necessary. The hypothalamus then resets the body’s temperature set point back to its normal range.
With the set point returned to normal, the body activates mechanisms to dissipate excess heat. Vasodilation, where blood vessels near the skin’s surface widen, increases blood flow, allowing heat to radiate away, often resulting in flushed, warm skin. The body also increases sweat production. As sweat evaporates, it carries heat away, providing a significant cooling effect. These actions lower the body’s temperature, bringing it back to its baseline.
When to Seek Medical Advice
While fevers are often a natural part of the body’s immune response, medical attention is sometimes advisable. For infants younger than three months, a rectal temperature of 100.4 degrees Fahrenheit (38 degrees Celsius) or higher warrants immediate medical evaluation. In children three to six months old, a rectal temperature exceeding 102 degrees Fahrenheit (38.9 degrees Celsius), or a lower temperature with unusual irritability or sluggishness, should prompt a call to a healthcare provider. For adults, a fever of 103 degrees Fahrenheit (39.4 degrees Celsius) or higher, or one lasting longer than three days, suggests the need for medical consultation.
Other indicators for seeking medical advice include a fever with symptoms such as a severe headache, stiff neck, rash, mental confusion, difficulty breathing, persistent vomiting, or seizures. These symptoms may signal a more serious underlying condition requiring prompt diagnosis and treatment. Always consider the individual’s overall condition and behavior, as these are important clues regardless of the specific temperature reading.