Fever Temperature

Marianne Dyson, April 2020

One of the major symptoms of COVID-19 is fever. A fever is defined as a temperature about 2˚F above normal. Next question is, of course, what is normal? It depends…

Though doctors and scientists have known for decades that body temperatures vary from person to person, 98.6˚F (37˚C) has been considered the average since the 1800s. But new data has reset the average to 97.9˚F. The lower average is attributed to less inflammation today than in the 1800s when many people suffered with infections and chronic illnesses such as TB. [Ref. “Forget 98.6” by Kristin Fischer.]

Thus, today, if someone’s temperature is 100˚F (37.8˚C) or higher, they may have a fever. The 100˚F value is what airport screeners use as a threshold to decide to detain someone in quarantine or keep someone from boarding a plane.

There are multiple reasons why a simple screening will yield false positives and miss many people who are sick. Even when the thermometer “guns” are held at the proper distance from the subject, the reading might be incorrect because of dust, heat sources (car or outside temperature), or because the person was exercising, drank strong coffee, or took medication. [Ref. “Thermometer guns…” by Morgan McFall-Johnson.]

Two other important factors affecting body temperature are age and gender. People over 65 are warmer (98.6˚F) on average than younger adults (97 to 99˚F) or babies (97.9 to 99˚F).   [Ref. “What is the Normal Body Temperature Range?” by Carissa Stephens.]

Mostly because women have a larger body surface to mass ratio and have more subcutaneous fat than men, women are generally hotter (96.3˚F to 99.5˚F) than men (95.9˚F to 99.5˚F). This explains why women are more likely to need extra blankets than men! [Ref. “Gender differences in thermoregulation” by Kaciuba-Uscilko, and Grucza.]

Also, the temperature of women of child-bearing age changes by about half a degree during the menstrual cycle. At the time of ovulation at mid cycle, temperature drops to its lowest for about three days. Women are most fertile during this time, leading to the “rhythm method” of planning or avoiding pregnancy. [Ref. “Basal body temperature for natural family planning.” Mayo Clinic Staff.]

Time of day and activity level also impact temperature. Temperatures are the lowest in the morning after at least three hours of sleep. Temperatures rise throughout the day and may be several degrees higher during periods of physical activity—especially if you’re an astronaut! (You knew I’d find a way to include space in this topic, right?!)

A study onboard the International Space Station showed that after two and a half months in space, astronauts’ core body temperature was 100.4˚F on average. This “space fever” is attributed to the difficulty of cooling off in the space environment. Sweat doesn’t evaporate as well in freefall, resulting in some astronauts’ temps spiking to 104˚F during exercise. [Ref. “Space Fever” by Charite-Universitatsmedizin.]

So temperature alone does not indicate fever. The only way to know for sure if YOU have a fever is to know your baseline temperature.  

To find my baseline, I gathered five different thermometers from around my house. My average turned out to be 97.8˚F, just a tad under average. [Ref.  “7 Types of Thermometers…” by Jeff Calaway.]

Five thermometers
Five thermometers found around my house provided temperature readings from 97.4˚F to 98.4˚F, with an average of 97.8 ˚F during the same 15-minute period. Digital thermometers were faster, but not more accurate than old-fashioned mercury ones. Photo by Marianne Dyson, 2020.

If I suspect a fever, the first thing I will do is to repeat the measurement in case I didn’t shake my (mercury) or reset my (digital) thermometer correctly, or I didn’t place it properly in my mouth or on my temple.

If I confirm a fever, I will then visit the CDC Self Checker to see if I should call my doctor and/or get tested for COVID-19.

Knowing my normal temperature range and recording it every day at the same time provides me a measure of comfort. I hope you give this a try and that this knowledge helps ease your mind a bit, too!

Writing about Space

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Speaking about Space

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Author: Marianne

Marianne Dyson is an award-winning children's author, science fiction writer, and former NASA flight controller. To invite her to speak or order her books, visit her website, www.MarianneDyson.com.