When the body’s temperature rises above its normal range, it often signals an underlying process, such as an infection. This elevated body temperature is known as a fever. Many individuals experience shivering, an involuntary muscle contraction, alongside this rise in temperature. Understanding the physiological mechanisms behind both fever and shivering helps clarify why these two responses are connected.
Understanding Body Temperature
The human body maintains a remarkably stable internal temperature, typically around 37 degrees Celsius (98.6 degrees Fahrenheit), through a process called thermoregulation. A small region in the brain, the hypothalamus, functions as the body’s primary thermostat, constantly monitoring and adjusting temperature. To cool down, the hypothalamus triggers responses such as sweating, which releases heat through evaporation. Conversely, to generate or conserve heat, it initiates mechanisms like muscle activity and the narrowing of blood vessels near the skin’s surface.
The Fever Process
Fever is a deliberate elevation of the body’s temperature, typically in response to an infection or inflammation. This process begins when substances called pyrogens enter the bloodstream. Pyrogens can originate from outside the body, such as components of bacteria or viruses, or they can be produced internally by the body’s own immune cells. These pyrogens signal the hypothalamus, causing it to reset the body’s temperature set point to a higher level. Consequently, the body perceives itself as being too cold relative to this new, elevated set point, even as its actual temperature begins to rise.
Why Shivering Occurs
Once the hypothalamus raises the temperature set point, the body activates mechanisms to reach this new, higher target temperature. Shivering is one of the primary ways the body generates additional heat. This involves rapid, involuntary contractions of skeletal muscles, which produce heat as a byproduct of muscle activity. Simultaneously, the body implements other heat-conserving responses, such as vasoconstriction. This process narrows the blood vessels in the skin, reducing blood flow to the surface and thereby minimizing heat loss to the environment. These combined efforts help the body achieve and maintain the elevated temperature demanded by the new hypothalamic set point.
When to Consult a Doctor
While fever and shivering are common responses, medical attention may be appropriate in certain situations. For adults, consulting a healthcare provider is advised if a fever reaches 39.4 degrees Celsius (103 degrees Fahrenheit) or higher. In infants younger than three months, a rectal temperature of 38 degrees Celsius (100.4 degrees Fahrenheit) or higher warrants immediate medical evaluation. A doctor should also be consulted if the fever persists for more than three to five days, regardless of age. Additionally, seek medical care if fever is accompanied by severe symptoms like difficulty breathing, a stiff neck, confusion, persistent vomiting, or an unexplained rash.