The 98.6℉ Myth: Why Everything You Think You Know About Body Temperature Is a Lie

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When you were kid, you probably knew that to score a magical sick day home from school, you needed to have a fever. When the thermometer came out of your mouth, it had to read higher than 98.6℉—the long-accepted "normal" human body temperature. (If you wanted to really seal the deal, you may have hoped to hit 100℉.) Since then, you may have used a temperature above 98.6℉ as a metric to work from home (or call out sick entirely).

But here's the thing: The average body temperature isn't actually 98.6℉—a fact that we've known for more than 25 years. The myth originated in the 19th century with a single doctor, and despite evidence to the contrary, it's persisted ever since.

THE GIANT—AND FAULTY—ARMPIT THERMOMETER

In 1851, Carl Wunderlich, the director of the hospital at Leipzig University, began going from room to room with a comically large thermometer in tow. He wanted to understand how body temperature is affected by different diseases, so in each room, he would hold the foot-long device in patients' armpits for a full 20 minutes, waiting for a temperature to register. Once it did, he'd note the temperature on the patient's chart (Wunderlich is thought to be the first physician to do so). He and his staff did this for years, repeatedly taking the temperatures of some 25,000 patients and logging them on their charts, until he had millions of readings. In 1868, he finally published this data in Das Verhalten der Eigenwarme in Krankheiten (On the Temperature in Diseases: A Manual of Medical Thermometry). He concluded that the average human body temperature was 98.6℉, underscoring the idea that fever is a symptom of illness, not a cause.

No one questioned Wunderlich's methods, or his average, for about 140 years. Then, in the early 1990s, internist Philip Mackowiak—a professor of medicine at the University of Maryland, a medical historian, and, apparently, a clinical thermometer junkie—saw one of the physician's instruments at the Mutter Museum in Philadelphia. He told the Freakonomics podcast that he'd always had doubts about the 98.6℉ standard. "I am by nature a skeptic," he said. "And it occurred to me very early in my career that this idea that 98.6 was normal, and then if you didn't have a temperature of 98.6, you were somehow abnormal, just didn't sit right."

Getting his hands on Wunderlich's thermometer—which the museum let him borrow—only deepened his doubts. The huge thermometer was unwieldy and non-registering, meaning, Mackowiak explained, "that it has to be read while it's in place." Not only that, but Wunderlich had used the device to measure temperatures in the armpit, which is less reliable than temperatures taken in the mouth or rectum. The instrument itself also wasn't terribly precise: It measured up to 2 degrees Centigrade higher than both ancient and modern instruments.

In 1992, Mackowiak decided to test Wunderlich's average. Using normal-sized oral thermometers and a group of volunteers, he determined that the average human body temperature actually hovers around 98.2℉. Mackowiak found that body temperature tends to vary over the course of the day, with its lowest point around 6 a.m. and its highest in the early evening. Body temperature can also fluctuate monthly (with the menstrual cycle) and over a lifetime (declining decade by decade with age), and may even be differentially linked to sex and race assignments. He concluded that normal body temperature is so unique to each person that it's almost like a fingerprint and, given that wide variation, not actually a very reliable indicator of illness.

As a result of his study, Mackowiak proposed raising the threshold for fever to 98.9℉ for temperatures taken in the morning (and 99.9℉ at other times). While it's a relatively minor change in terms of actual degrees, this fever threshold is actually lower than the CDC's, which is a temperature of 100.4℉ or higher.

There are potential real-life consequences in this gap, for everyone from students (who'd have to attend school with what would be considered a low-grade fever by Wunderlich's 98.6℉ standard) to employers and daycares (who use temperature to set attendance policies). What's more, anyone who is actually sick but ignores a low-grade fever—one that meets Mackowiak's threshold but still falls under the CDC's—could pose a risk to people with compromised immune systems trying to avoid unnecessary exposure to illness in public places.

THE BALANCING POINT

There's a reason the average trends near 98℉ instead of 92℉ or 106℉. As endotherms, mammals expend a great deal of energy maintaining body temperature when compared with cold-blooded creatures. To find and conserve a just-right body temperature, central nervous system sensors gather data (too warm? too cold? just right, Goldilocks?) and send that information to the pebble-sized hypothalamus near the base of the brain. There, the data is converted into action: releasing sweat and widening the blood vessels if too warm; raising metabolism, constricting the blood vessels, and inducing shivering if too cold.

According to a study by Aviv Bergman and Arturo Casadevall in the journal mBio, the precise balancing point for ideal body temperature is the sweet spot where the metabolic cost for all this thermoregulation balances with the evolutionary advantage of warding off fungal disease. (While warm-blooded animals are prone to bacterial or viral infections, they rarely experience fungal infections because most fungi can't withstand temperatures above 86℉. Cold-blooded animals, on the other hand, are prone to all three.) For Bergman and Casadevall, this benefit even explains what tipped Darwin's scales in favor of mammals, allowing them to edge out other vertebrates for dominance after the Cretaceous-Tertiary mass extinction wiped out the dinosaurs.

Of course, rules call for exceptions, and the one place where human body temperature demonstrates sustained elevation is outer space. Astronauts on prolonged missions clock significantly higher average body temperatures than they do when terrestrial—even up to 104℉. This so-called "space fever" is probably a product of some combination of radiation exposure, psychological stress, and immune response to weightlessness. Researchers believe this phenomenon could yield crucial information about thermoregulation—and may even offer insight into how humans might adapt to climate change.

WHY THE MYTH PERSISTS

It's been 26 years since Mackowiak's study, yet the newer data has not taken hold among medical professionals or the public. What gives?

Mackowiak tells Mental Floss that he finds it a bit mystifying that the myth persists, especially since many people, when pressed, know that the so-called "average" temperature varies. Part of the problem may be psychological: We cling to beliefs despite evidence to the contrary—a phenomenon called belief perseverance [PDF]. It's a significant force upholding a surprising number of medical myths. The idea humans should drink eight glasses of water a day? Not science. Sugar causes hyperactive behavior? Nope. Reading in dim light harms eyesight? Not really.

Unlearning persistent myths—especially ones loaded with the weight of medical authority—is difficult. "Deep down, under it all," Mackowiak says, "people want simple answers for things."

10 Facts You Should Know About Epilepsy

Madrolly/iStock via Getty Images
Madrolly/iStock via Getty Images

While the signs of some chronic illnesses are vague or invisible, epilepsy symptoms can be hard to miss. The neurological disorder is characterized by recurrent epileptic seizures, or periods of excessive or overlapping activities in the brain. It also comes with a stigma: Patients who exhibit epileptic seizures have been accused of being violent, mad, and even possessed. Those misconceptions are sometimes more harmful than the epilepsy symptoms themselves. With proper treatment, people with the condition often lead safe, happy lives. Here are some more facts.

1. Epilepsy has fueled superstitions for centuries.

Before modern medicine, cultures around the world mistook epileptic seizures for spiritual possession. There’s even a passage in the New Testament of the Bible where Jesus performs an exorcism on a boy having an apparent epileptic fit. The ancient Greeks [PDF] believed seizures were a punishment sent from the gods, and therefore considered them sacred. We now know that seizures originate in the brain, but the superstitions that surround them persist.

2. Epileptic seizures are caused by a neurological imbalance.

The brain is controlled by neurons: cells that carry electrical impulses that allow us to process our environment. Some neurons stimulate other brain cells, while others tell them to calm down. This balance is what allows us to function normally. In people with epilepsy, too many stimulating or calming neurons fire at the same time, causing epileptic seizures.

3. There are different types of epileptic seizures.

When most picture someone having a seizure “seizing up,” losing consciousness, and convulsing uncontrollably. These are the characteristics of grand mal or tonic-clonic seizures, but it’s not the only form they take.

Generalized seizures are caused by activity in both hemispheres of the brain, and they include tonic-clonic seizures, as well as absence seizures (brief loss of consciousness), myoclonic seizures (random muscle jerks), and more. Focal seizures occur in only one region of the brain and can be simple—limited to twitching and odd feelings, tastes, or smells—or complex, where sufferers experience a temporary loss of awareness.

4. Not all seizures are signs of epilepsy.

Spontaneous, non-epileptic seizures happen for a number of reasons, ranging in seriousness from brain tumor or stroke to low blood sodium or lack of sleep. A patient is usually diagnosed as epileptic after they’ve experienced two or more seizures, or if they have a positive result on a diagnostic neurological test. The most common test, an electroencephalogram (EEG), monitors electrical activity in the brain.

5. Epilepsy causes vary from person to person.

A person can develop epilepsy for a variety of reasons. In some cases, mutations in the genes related to regulating neurons can make some people more vulnerable to the environmental factors that cause the disorder. Other causes include brain damage, infectious diseases like AIDS, and developmental disorders like autism. But in roughly half of all cases, the condition is cryptogenic, which means doctors can’t pinpoint a specific cause.

6. Outside stimuli can trigger epileptic seizures.

Things that affect brain function, like drinking alcohol, taking drugs, and not getting enough sleep, can make someone more vulnerable to having epileptic fit. Other triggers are much harder to avoid: People with reflex epilepsy get seizures as a reaction to stimuli, such as flashing lights or even music.

7. Auras can signal an impending seizure.

Warning signs known as auras can take the form of a strange smell or taste, a sudden wave of fear or joy, a feeling of déjà vu, or random muscle twitches. Auras are technically focal seizures, which are seizures the sufferer is aware of, and though they often precede bigger seizures that trigger a loss of consciousness, they can also happen on their own.

8. Temporary paralysis sometimes follows an epileptic seizure.

After their seizure has stopped, patients may experience full or partial paralysis, usually on one side of their body. The loss of motor function can last anywhere from 30 minutes to 36 hours, but most of the time it doesn’t exceed 15 hours. This phenomenon is named Todd’s paralysis after Victorian physician Robert Bentley Todd, who first described it.

9. Few epileptic seizures are fatal.

The biggest threat during an epileptic fit is injury from falling down and convulsing in an unconscious state, but the majority of seizures don’t cause serious harm on their own. The exception is tonic-clonic status epilepticus, which is the name for a seizure that lasts five minutes or longer. These are considered emergency seizures and can result in brain damage or death [PDF].

10. Epilepsy can be treated with vagus nerve stimulation.

Epilepsy is highly treatable with a number of methods, from drugs to brain implants. Many patients take anti-seizure medications that balance neural signals and prevent seizures from happening. Surgery to remove the area of the brain where seizures typically begin is another form of treatment. Other options include a high-fat, low-carb diet, which can stabilize neuron function, and vagus nerve stimulation, which uses implants to send electric pulses up the vagus nerve in the neck to regulate brain activity.

CVS Pulls Zantac and Similar Heartburn Medications From Stores Over Cancer Concerns

Drew Angerer/Getty Images
Drew Angerer/Getty Images

On September 28, CVS Pharmacy announced that it’s pulling some heartburn medications from its shelves until further notice, following an alert from the Food and Drug Administration that they may contain a cancer-causing ingredient.

CNN reports that the medication in question is ranitidine, and CVS will stop selling its store brand version and the more commonly known brand-name version Zantac. Though tests are still ongoing, the FDA has found that ranitidine contains N-nitrosodimethylamine (NDMA), which is a “probable human carcinogen,” according to a statement from CVS.

CVS’s voluntary suspension of sales is a “better safe than sorry” course of action—the FDA hasn’t issued a formal recall of Zantac/ranitidine or even suggested that users stop taking the medication. In its statement, CVS says that “the levels [of NDMA] that FDA is finding in ranitidine from preliminary tests barely exceed amounts found in common foods.” According to the Agency for Toxic Substances and Disease Registry, a division of the U.S. Department of Health and Human Services, NDMA is also found in tobacco, cured meats, beer, fish, cheese, and even the air we breathe [PDF].

Ranitidine is a type of H2 receptor blocker, which decreases heartburn and acid reflux symptoms by preventing stomach cells from releasing excess acid. It isn't the only H2 receptor blocker on the market, so this might be a good time to consult your healthcare provider or pharmacist about switching to a different one, like Pepcid (famotidine) or Tagamet (cimetidine).

The FDA said in a statement that it will continue investigating the potential risk of taking ranitidine and share its findings when available.

[h/t CNN]

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