Sweating when sick is a common and often uncomfortable symptom that signals a biological process is taking place within the body. This profuse perspiration is typically a sign that the body is actively working to regulate an elevated internal temperature, most often caused by an infection. The sensation you feel is the physical manifestation of your body’s temperature control system, centered in the brain, attempting to return to a balanced state. Understanding this process involves looking at how the body first raises its temperature to fight the illness and then how it rapidly cools itself down.
How the Body Raises Its Temperature
The immune system initiates the process of fever when it detects invading pathogens like bacteria or viruses. Specialized immune cells, such as macrophages, respond by releasing powerful signaling molecules known as endogenous pyrogens. These chemical messengers travel through the bloodstream to the brain, specifically targeting the hypothalamus, which acts as the body’s central thermostat.
Upon receiving the pyrogen signals, the hypothalamus instructs the body to raise its temperature set point by stimulating the synthesis of prostaglandin E2 (PGE2). This means the body’s preferred operating temperature is suddenly higher than its actual temperature, causing a sensation of coldness even if the core temperature is already slightly elevated. To meet this new, higher set point, the body begins heat-generating activities, such as shivering and chills, and heat-retaining actions like peripheral vasoconstriction.
The body works to reach this new, higher temperature, which is a deliberate defense mechanism. Elevated temperatures make it more difficult for certain pathogens to survive and can also enhance the activity of some immune cells. The chills and shivering are the physical signs that your muscles are contracting rapidly to generate the necessary heat to reach the hypothalamic set point. Once the body temperature aligns with the new, higher set point, the chills and shivering typically stop, and the fever plateaus.
The Mechanism of Cooling Down
The profuse sweating begins when the immune system starts gaining control over the infection or when fever-reducing medication is effective. At this point, the hypothalamus “resets” the body’s temperature set point back to its normal, pre-illness level. Because the body’s actual core temperature is still elevated from the fever, it is now overheated relative to the new, lower set point.
The body must then rapidly eliminate this excess heat to avoid overheating, a process often referred to as “the fever breaking.” Two primary mechanisms are immediately activated to facilitate this rapid cooling. The first is vasodilation, where the blood vessels near the skin’s surface widen significantly. This allows warm blood to flow closer to the skin, transferring heat from the core to the surface through convection.
The second and most noticeable cooling mechanism is diaphoresis, or excessive sweating. The eccrine sweat glands are stimulated to secrete moisture onto the skin’s surface. As this moisture evaporates, it carries thermal energy away from the body, leading to a cooling effect. This evaporative cooling is the main reason a person feels drenched and clammy as the fever subsides.
Sweating Not Related to Fever
While breaking a fever is the most common cause of sweating during illness, other biological processes can also trigger it. Severe infections often induce a stress response, causing the sympathetic nervous system to activate the “fight-or-flight” response. This releases hormones like adrenaline and cortisol, which can directly stimulate sweat glands, resulting in clammy “cold sweats” that are unrelated to temperature regulation.
Night sweats are associated with a persistent inflammatory state rather than the breaking of an acute fever. Chronic infections, such as tuberculosis or HIV, can cause the continuous release of inflammatory cytokines, which disrupt the body’s thermoregulation cycle, particularly during sleep. Additionally, mild physical exertion or pain experienced while sick can trigger the sympathetic nervous system, leading to temporary periods of increased perspiration.