The Myth of 98.6° F

Medical research reported in 1992 shows that the mean human body temperature is actually 98.2° F rather than 98.6°. The range for normal (healthy) human body temperature is 97.5° F (36.2° C) to 98.9° F (37.2° C), but up to 5 percent of the population have a body temperature that falls outside this range (my own average body temperature, for example, is a cool 96.8°). Basal metabolic rate is one factor that can influence this. Additionally, very young infants have less ability to regulate their body temperature in cool environments and are more prone to hypothermia; body temperature also tends to decline with age, so that those over 65 may have an average temperature 1 to 2 degrees lower than individuals under 40.

Even in a single individual, body temperature can vary throughout the day by as much as 1 to 2 degrees. It tends to be coolest in the early morning (2am to 4am), and warmest in the late afternoon (4pm to 6pm), even among those who work at night and sleep during the day.

Body temperature can also be normally affected by such things as extreme physical activity, ovulation and pregnancy in women, and smoking. It is also affected by the part of the body measured: The body's extremities are colder than the body core; and temperature taken in the mouth, while convenient, tends to be less accurate (due to improper thermometer placement, breathing, recent consumption of hot or cold beverages, etc.) than temperature measured rectally or tympanically, but more accurate than axillary measurements.

Temperatures Above Normal

As noted above, body temperature can be affected by a variety of activities and conditions. Strenuous exercise can temporarily raise body temperature to as high as 103° F, while extreme exercise, such as a marathon, can raise body temperature temporarily as high as 107° F. When the body core temperature reaches 105° F or higher, heat exhaustion followed by heat stroke or hyperthermia (also known as hyperpyrexia) can occur, especially where dehydration (in which case the body can not produce enough sweat to sufficiently cool down) also is present. Additionally, the use of some drugs — Ecstasy (MDMA, also called E, X or XTC), for example — can cause body temperature to rise to dangerously high levels.

Left untreated, heat stroke can lead to permanent brain damage, kidney damage and/or circulatory collapse resulting in death.

Sustained elevated body temperature associated with disease or infection is called fever. A fever of 102° F or lower is defined as low grade, while that above 103 ° F is defined as high grade. Fevers that increase and decrease regularly are said to be cyclic, while those that have sudden sharp increases and then drop are called spiking fevers.

There is also a medical condition known as malignant hyperthermia, an inherited condition that can cause a rapid rise in body temperature to dangerous levels when the individual is given general anesthesia or takes certain types of muscle relaxants.

Temperatures Below Normal

Hypothermia is the name given to the very dangerous condition when core body temperature drops to below 96° or 95° F (sources vary). Acute hypothermia most often is caused by a sudden, pronounced such drop, through immersion in very cold water, for example, or exposure to cold weather. Chronic hypothermia, due to underlying disease, is a rarer condition.

There are three main stages of hypothermia, depending on the range into which the core body temperature falls and the symptoms evidenced:

  • Mild hypothermia, body temperature between 98.6 and 96° F: involuntary shivering; difficulty with complex motor functions, but can still walk and talk
  • Moderate hypothermia, body temperature between 95 and 93° F: dazed consciousness, loss of fine motor control, slurred speech, violent shivering, irrational behavior
  • Severe hypothermia, body temperature between 92 and 86° F and below: shivering occurs in waves, person falls to ground, muscle rigidity, pale skin, dilated pupil, increased pulse rate. At 90° F the body attempts to go into a form of hibernation, shutting down all peripheral blood flow and reducing heart and respiration rates. At 86° F the person looks dead, but it still alive. Death usually occurs before body temperature reaches 78 to 75°.
  • Normal Temperatures for Other Species (° F / ° C)

    • Cat: 100.4-101.6 / 38.0-38.5
    • Dog: 100.9-101.7 (one source said 102) / 38.3-38.7 (38.9)
    • Hamster: 98-101 / 36.2-37.5
    • Guinea pig: 99-103 / 37.2-39.5
    • Stallion: 99.7 / 37.6
    • Mare: 100 / 37.8
    • Rabbit: 103.1 / 39.5
    • Pig: 102.5 / 39.5
    • Goat: 102.3 / 39.1
    • Sheep: 102.3 / 39.1
    • Dairy cow: 101.5 / 38.6
    • Monotremes: 87.8-89.6 / 31-32
    • Camels, Oryx, Gemsbok, etc.: daytime 105.8 - nighttime 98.6 /daytime 41 - nighttime 37 (only in wild; in laboratory conditions, their temperatures do not show these fluctuations)
    • Hibernating Arctic ground squirrel: 28.4 / -2
    • Sparrow: 105.8 / 41
    • Bird range: 100-112 / 30-44

    Sources consulted in compiling this writeup included:

    • "What's Normal? Temperature, Gender, and Heart Rate" (www.amstat.org/publications/jse/v4n2/datasets.shoemaker.html)
    • "Is Your Body Temperature Normal?" (www.intelihealth.com)
    • "Physiology of Body Temperature" (www.fevers-in-pets.com/html/body_temp.html)
    • "Hot Bodies" (newscientist.com)
    • "Sleep Tight" (Oconee Forest Park article archive)
    • "Body Temperature" (Provet healthcare information)
    • Hypothermia section from "Just the Berries for Family Physicians" (www.theberries.ns.ca)

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