When the body encounters an infection or inflammation, a fever often develops as a natural defense mechanism. This elevated body temperature signals that the immune system is actively working to combat the threat. A common observation during the recovery phase is a sudden onset of sweating, which indicates the fever is breaking. This phenomenon is a physiological response aimed at restoring the body’s normal temperature.
Understanding Your Body’s Thermostat
The human body maintains a stable internal temperature, typically around 37°C (98.6°F), through a process called thermoregulation. This regulation is primarily managed by a region in the brain known as the hypothalamus, often referred to as the body’s thermostat. The hypothalamus continuously monitors the body’s core temperature and compares it to a specific “set point.” When the actual temperature deviates from this set point, the hypothalamus activates various mechanisms to balance heat.
How Fever Changes the Thermostat Setting
During an infection, substances called pyrogens trigger the onset of fever. These pyrogens can originate from outside or inside the body. These chemical signals travel to the hypothalamus and induce the synthesis of prostaglandins, particularly prostaglandin E2 (PGE2). PGE2 then raises the body’s temperature set point to a higher level.
With this new, elevated set point, the body perceives its current temperature as too low. To reach the higher target, the hypothalamus initiates heat-producing and heat-conserving responses. This can include shivering, which generates heat, and vasoconstriction, which reduces heat loss. These actions cause the body temperature to rise until it matches the new set point, resulting in a fever.
The Moment the Fever Breaks
A fever begins to break when the immune system successfully overcomes the infection or the inflammatory process subsides. As the underlying cause is resolved, the production of pyrogens decreases. This reduction in pyrogenic signals allows the hypothalamus to reset its temperature set point back to its normal level.
At this point, the body’s core temperature is still elevated, but the internal thermostat now perceives this temperature as too high. To rapidly bring the body’s temperature down, the hypothalamus triggers cooling mechanisms. This transition is often marked by a feeling of warmth and profuse sweating.
Why Sweating Cools You Down
When the hypothalamus resets the temperature set point to normal, the body activates efficient cooling processes. One such mechanism is vasodilation, where blood vessels close to the skin’s surface widen. This increased blood flow brings warm blood from the body’s core to the periphery, allowing heat to dissipate.
Simultaneously, the sweat glands become highly active, releasing a significant amount of sweat onto the skin. The primary cooling effect of sweating occurs through evaporation. As sweat evaporates from the skin, it absorbs substantial heat energy from the body, carrying that heat away. This evaporative cooling rapidly sheds excess heat and returns the body to its normal temperature, explaining the noticeable sweat.