What is Pyrexia? | Definition, Causes & Symptoms

Pyrexia: A Natural Immune Response

Have you ever wondered how we survived before the age of medicine? With so much controversy over vaccinations and the overuse of antibiotics causing resistant strains of superbugs, what did we do before we had medicine and access to healthcare?

Fortunately, we were designed with a complex mechanism of our own immune system called pyrexia. Pyrexia is a rise in the body's core temperature, otherwise known as a fever. It is a mechanism developed by the immune system to reduce the severity of illness by preventing bacteria and viruses from multiplying. This activation of the immune system has worked for centuries before medicine was invented. Most individuals view a fever as something that is bad or harmful, but it is a sign that our body is working in our favor to fight disease.

How Does Fever Work?

To understand what a fever is, we first need to discuss normal temperature. For example, a goat's core temperature is 105 degrees Fahrenheit, and a human's is 98.6 degrees Fahrenheit. I bet you're wondering how the heck they got a goat to put a thermometer in its mouth. Bad news: They probably had to resort to a rectal thermometer!

The temperature varies slightly depending on where in the body it was measured. For example, a rectal thermometer measures the body's internal core temperature by inserting a thermometer into the rectum.

An axillary temperature measures the temperature under the armpit, which tells the temperature on the surface of the skin. An oral temperature is taken by placing a thermometer under the tongue, which measures the temperature in the oral cavity (mouth).

So the temperature taken rectally (internally) will be higher and more accurate than if taken in the mouth or on the skin. Despite this, taking one's temperature rectally is far less common - it is certainly more convenient to take a temperature under the armpit or in someone's mouth as opposed to rectally at every doctor's appointment.

The Body's Internal Thermostat

The body's temperature actually fluctuates throughout the day and in response to activity and sleep patterns. The usual culprits - those not related to bodily injury or disease - are exercise, eating, medication, menstrual cycle, hot weather and humidity.

We have an internal thermostat called the hypothalamus, which is a small gland located in the brain. This gland functions as a part of the nervous system, sending signals out to the mechanisms that heat and cool the body. The hypothalamus responds to the presence of biochemical communicators called pyrogens, which are released into the bloodstream from injured body tissues or from the presence of disease-causing microorganisms.

The pyrogens cause the hypothalamus to increase the body temperature. This works to lower the amount of bacteria and virus in the body, because the high temperature makes it difficult for them to multiply and replicate. The heating process acts by shunting blood away from the extremities to the internal core of the body. This induces shivering that also raises temperature.

Treatment of Pyrexia

In most cases, fever does not need to be treated, because it is a sign that the body is working hard to defeat an infection or disease. Children usually have more fevers due to an immature immune system, and the American Academy of Pediatrics recommends easing uncomfortable symptoms as opposed to bringing a child's temperature back to a normal range. In much the same way, we don't go around medicating baby goats with fever; instead, we usually take a watch-and-see approach and let the fever run its course and fight off the bacteria or virus.

An antipyretic, such as over-the-counter ibuprofen or acetaminophen, may be given for pain or excessive crying related to a fever. Non-medical treatment for fevers include removing layers of clothing, lowering room temperature, applying a cool washcloth or soaking in a lukewarm bath.