The Argument for Letting a Fever Run Its Course
It may lead to better outcomes, some experts say
In the 1970s, a University of Michigan physiologist named Matthew Kluger conducted a series of experiments in which he and colleagues infected iguanas with illness-causing bacteria. Their goal was to study how these infections responded to fever.
In one experiment, the sick iguanas were given access to heat lamps, which helped the cold-blooded lizards raise their body temperatures in ways that mimicked a fever. All but one of them took advantage of the heat lamps, and the outlier was the lone animal to die of its illness. In another experiment, Kluger gave sick iguanas fever-reducing drugs. Five of these iguanas still managed to develop a fever, and those five lived. Meanwhile, the seven that did not develop a fever died.
Fevers are no fun — for lizards or for human beings. In people, fevers are associated with sweating, chills, and body aches, as well as weakness, nausea, breathing problems and, in some cases, strange dreams or hallucinations.
Why put up with all that? Many doctors say you shouldn’t. Take a fever-reducer like aspirin or acetaminophen and feel better. “Fever is your body’s way of telling you that something’s wrong, and you need to do something about it,” says Dr. Lee Riley, a professor of infectious diseases at the University of California, Berkeley School of Public Health. A fever not only causes unpleasant symptoms, but it also places added stress on the body — stress that may impair its ability to recover.
“Every aspect of your immune system works better at a higher temperature.”
The Covid-19 crisis has a lot of people on the lookout for fever. Along with a cough and shortness of breath, fever is one of the virus’s primary symptoms, according to the Centers for Disease Control and Prevention (CDC). But the CDC does not explicitly recommend taking fever-reducing drugs to treat the virus. And not all doctors believe that a fever is something unpleasant to be suppressed or snuffed out.
Some argue that, rather than impeding the body’s ability to get better, a fever actually helps the body rid itself of harmful pathogens. “Every aspect of your immune system works better at a higher temperature,” says Dr. Paul Offit, a professor of vaccinology at the University of Pennsylvania, and a professor and attending physician in the Division of Infectious Diseases at Children’s Hospital of Philadelphia.
Take a pill to reduce a fever, Offit says, and you’re more likely to prolong or worsen your illness. And there’s research — in animals, and also in people — to back up his claims.
The fever controversy
The Greek physician Hippocrates, who is often called the father of Western medicine, wrote more than 2,000 years ago about the beneficial effects of fever. In the 17th century, the English doctor Thomas Sydenham called fever “nature’s engine which she brings into the field to remove her enemy.”
During the late 1800s, a German physician named Carl von Liebermeister made a name for himself by studying fevers and their response to cold baths and other treatments. While Liebermeister thought that fevers could be dangerous if they raged too high or lasted too long, he also believed that short or moderate fevers were helpful.
But at some point between Liebermeister’s day and the present, mainstream medicine embraced the belief that a fever — usually defined as a temperature of 101 degrees or higher — places added and unnecessary stress on a sick person’s system. “[Doctors] seem to possess an ingrained philosophic opposition towards fever, prompting a knee-jerk response to treat that is not supported by high-level evidence,” write the authors of a 2015 review study in the Journal of Thoracic Disease.
One 2015 study in the American Journal of Clinical Nutrition examined the effects of acetaminophen (Tylenol) among people with fever in a hospital intensive care unit (ICU) setting. Those who got acetaminophen fared no better than those who got a placebo, the study found.
“Anything that walks, crawls, and flies on this planet can make a fever, so I think it’s reasonable to conclude that this response is there for a reason.”
Another study, published in 2005, examined the effects of fever-reducing drugs and cold blankets among 82 people in an ICU. In about half of these people, doctors and nurses treated fever “aggressively,” meaning they used drugs and cold blankets whenever a patient’s temperature reached 101.3 degrees. In the other half, they treated fever “permissively,” meaning they only took action when a person’s fever reached 104 degrees. The study had to be ended early because seven of the people in the aggressive-treatment group died, compared to just one in the permissive group.
To date, the evidence for or against the use of fever-reducing drugs is mixed — and also inchoate. And that’s doubly true when it comes to a virus like Covid-19, which medical experts have only begun to study intensively. But some, like University of Pennsylvania’s Offit, say there’s reason to believe these drugs do more harm than good.
The argument for letting a fever run its course
“Anything that walks, crawls, and flies on this planet can make a fever, so I think it’s reasonable to conclude that this response is there for a reason,” Offit says.
He points to research that has found that neutrophils, which kill infectious bacteria, seem to work better at elevated temperatures. Research also suggests that antibody-producing B-cells and infection-clearing T-cells work better when the body’s temperature is elevated. (It’s worth noting that Offit helped invent a patented rotavirus vaccine, and he’s the author of a book about the myth of the vaccine-autism link, which has made him a major target for those in the anti-vaccine movement. In other words, he is not someone who broadly rejects medical intervention in favor of letting nature do its thing.)
If a fever is so helpful, why are fever-reducing drugs so popular among both doctors and laypeople? “For one thing, they make people feel better, which provides the false sense that they’re treating the underlying problem,” he says. There’s also a popular belief that a very high fever can cause brain damage. But Offit says this is a misconception, and research again backs him up on this.
He also says that many parents worry about a child who has a fever, and that a fever can cause seizures in very young kids. But these “febrile” seizures, as they’re called, do not cause any lasting damage. “They’re hard to watch, but they don’t cause any permanent [issues],” he says.
So, the big question: Should people who develop a fever take something for it? Offit says no. “Unless you’re in the hospital for another condition like severe heart or lung disease — something that may make it difficult for your system to handle the metabolic stress of a fever — you should let a fever run its course.” (University of California, Berkeley’s Riley, who doesn’t share Offit’s views on fever-reducing drugs, says he also doesn’t know of any lasting harm that could result from letting a fever run its course.)
Even for people who develop a high fever — 104 degrees or above — and even for those who believe that they may have Covid-19, Offit says he doesn’t advise taking a fever-reducer, although people in these situations may still need emergency medical attention. (The CDC does not list a high fever as cause to seek medical attention for those who may have Covid-19.)
“It’s more important to pay attention to other worrisome symptoms like difficulty breathing or feeling quite ill even after the fever has come down,” he says. In other words, a high fever alone isn’t a reason to rush to the ER.
“With a fever, your immune system works better,” he argues. “So why cripple that?”
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