Child with thermometer in her mouth

Fever is a mighty engine which Nature brings into the world for conquest of her enemies.”

— Thomas Sydenham

The occasional abnormal elevation in body temperature associated with infection is as much a part of the human condition as abstract thought or the desire to lose weight without exercise or cutting calories. Commonly known as fever, this powerful yet misunderstood physiologic response has been documented in a variety of animal species including fish, reptiles and of course humans. We have all had fever at least once in our lives, and probably several times. And many of us have undoubtedly spent a few anxious nights cradling febrile little ones, afraid more of the repercussions of the fever itself than the potential sequelae of the underlying cause.

Along those lines, fever is one of the most common reasons for parents to seek medical care for their children, with roughly a third of pediatric acute care visits related to it, as well as a frequent impetus for late night nursing calls to sleepy hospitalists. Actually only about half of after-hours calls are about fever but who’s counting. Unfortunately most medical professionals, including many pediatricians, have a poor understanding of the pathophysiology of fever, and their panicked approach to its management in many children involves unnecessary laboratory tests, imaging studies, and doses of broad spectrum antibiotics. It also adds to parental anxiety and helps to establish a vicious cycle as patients of over worried caregivers tend to undergo more aggressive evaluation and treatment.

What isn’t fever?

Any discussion of what fever is must first be tempered by information on what fever isn’t. Fever is not hyperthermia. Hyperthermia is not a physiologic response to infection but instead is overheating despite our thermostat (I’ll get into this in a bit) being set at normal. Hyperthermia occurs when we retain excess heat from an external source, such as when a young child is forgotten in the car on a hot Louisiana Summer day, or when there is overproduction of heat caused by a reaction to certain medications. A diagnosis of hyperthermia carries with it significant risk of direct morbidity and mortality while fever rarely leads to direct harm. Perhaps some of the fear experienced by the mere thought of febrile children stems from the muddling of these two concepts. This post is about fever, not hyperthermia.

The physiology of temperature

The temperature of our bodies is amazingly steady despite significant variations in environmental temperature and physical exertion. This is achieved by an amazing interplay of our autonomic nervous and endocrine systems as well as some evolved instinctive behaviors. The thermoregulatory center of our bodies is the hypothalamus. It can be thought of as our “thermostat” and it maintains a temperature set point by balancing heat production with heat loss. We primarily produce heat by metabolic activity in the liver and muscle while heat is lost through the skin and lungs.

What is fever?

Fever occurs when our set point is raised above the current body temperature and is a homeostatic process. When the body is exposed to infectious organisms such as viruses and bacteria, a number of so-called pyrogens (another name for fever is pyrexia) are produced as part of the inflammatory response. These pyrogens can then act on the thermostat to raise the temperature set point by release of prostaglandin, primarily prostaglandin E2.

Now here comes the really fascinating stuff. Once the set point is raised, heat generating actions are taken by the body to raise core temperature to that new point and we enter the “chill” phase of fever. We increase cellular metabolism in a number of areas but the most dramatic response occurs in skeletal muscle. We conserve heat by constricting the blood vessels in our skin, decreasing the supply of warm blood to our extremities. In other words, we feel cold and we shiver. The evolved behavioral response should be obvious at this point. We grab the blankets and crank up the heat. All this happens before we actually have a measurable increase in our body temperature.

How high our body temperature goes with fever is limited by a number of factors, largely genetic or specific to the inciting infectious organism. But there is a negative feedback mechanism that involves production of cryogens which serves to keep things in check. When the illness resolves, or when antipyretic medications that target production of prostaglandins are given, the temperature set point returns to normal. This leads to the “flush” phase of fever. The blood vessels in our skin open up, bringing more warm blood to the surface to increase dissipation of heat via sweating, our cellular metabolism decreases, and we kick off the blankets. No more fever.

What is fever phobia?

When I take care of patients with fever I see a wide variety of parental reactions, ranging from reasonable concern to extreme worry, even terror occasionally. My personal experience is that the typical response is much closer to the latter. I always make a point to ask parents what they are worried about and I get a range of responses, from continued discomfort to brain damage to death. Again, anecdotal experience has led me to believe that folks are far more worried about fictional serious complications of fever than mere fussiness or malaise. At the core of these concerns is the misconception that the elevation in temperature represents a potentially dangerous disease in and of itself rather than a relatively benign symptom resulting from an infectious process. This is fever phobia and it has the potential for serious, even deadly, repercussions.

The number of blatant misconceptions regarding childhood fever is truly staggering. Since the 1980’s, when Barton Schmitt published the seminal paper on the subject of fever phobia in the American Journal of Diseases of Children, there have been several additional studies confirming and cataloging the causative factors and potentially dangerous resulting behaviors. These studies have shown that fever phobia exists in both parents and pediatric medical professionals.

Schmitt found that 94% of parents thought that fever could cause harmful side effects. It can’t, except very rarely in extremely critically ill children secondary to the increased metabolic demand. 63% of parents were very worried about serious direct harm from fever with 18% believing that brain damage could occur with temperatures less than 102 degrees. 16% believed that temperatures could rise to 110 to 120 degrees if untreated. Fever does not cause brain damage, hearing loss, blindness, etc. And it cannot rise above the rare 107 degrees (remember those cryogens?). Even then it does not directly harm the body. I imagine that one would feel pretty miserable however.

But that was in 1980. Things have changed, right? Not really. A 2001 paper revisiting fever phobia published in Pediatrics revealed that 91% of caregivers thought fever could cause harmful side effects including seizure (32%), brain damage (21%) and death (14%). Coma and blindness also made the list. With the exception of febrile seizures, a common and benign entity seen only in young children, fever just doesn’t do these things.

More than half of caregivers were very worried about significant harm with many worried even about temperatures less than 100 degrees. That isn’t considered a fever by pediatricians. More than half of caregivers checked temperature every hour (or more frequently!) during illness. My memory fails me, but I imagine two dozen rectal temperatures in a day is uncomfortable, and they certainly can cause injury. Taking the temperature of an older child may not require a rectal thermometer, but it is excessive, and children need sleep. But 85% of caregivers would wake sleeping children to give antipyretics (please don’t do that). A quarter of caregivers gave antipyretics for temperatures not considered a fever. Many children with temperatures of even 101 or 102 degrees aren’t symptomatic.

Here is where it gets dangerous. More than half of caregivers dosed antipyretic medications too frequently. Many studies done since 2001 have confirmed that parents frequently dose antipyretics incorrectly, putting their children at risk for serious liver and kidney injury. Unwarranted fear of fever leads to unnecessary medications, and if a dose that is too high is given too frequently, well, you get the picture. Nearly three quarters of caregivers admitted to the use of sponging to reduce fever, a practice which is ineffective even when done in a safe way. Two thirds of these caregivers however sponged incorrectly, using cool or cold water, or even rubbing alcohol. The former can causes discomfort and impede the ability to dissipate heat by constricting skin blood vessels, and the latter can cause toxicity and death.

Whose fault is fever phobia?

Parental fever phobia, which exists across socioeconomic classes, is strongly reinforced by the actions of pediatric medical professionals who are widely considered to be primary resources on the subject. Fever is often the first symptom we ask about and the first vital sign we check. We emphasize that our lab and imaging investigations are necessary because of the elevated temperature. We tend to treat any and all fever with antipyretics like acetaminophen and ibuprofen. Fever also plays a large role in discharge instructions from emergency departments and inpatient facilities, which commonly contain warnings to call or return if fever develops or persists.

Yet we often give incomplete, inconsistent and even incorrect information. That is when we actually give any information at all. In the early 1990’s, May and Bauchner looked into the role pediatricians play in fostering the development of fever phobia. They performed a survey of pediatricians in Massachusetts which found that 10% almost never discussed the definition of fever, 25% almost never discussed the effects of fever and 15% almost never discussed the cause of fever.

The survey revealed incongruence between the education of families and the practice of pediatricians. Pediatricians for the most part agreed that parents should not wake a sleeping child to check temperature or give antipyretics, but the majority advocated treating low and likely asymptomatic temperatures. These mixed messages remain in existence today. But it gets worse. In the same survey, May and Bauchner found 65% of pediatricians believed that fever could be dangerous with 21% listing brain damage as a potential complication. Just over a quarter of them listed death as a possible result of the fever itself, not the disease actually causing the fever.

In 2000, Mayoral et all published survey results in Pediatrics revealing that nearly a decade later pediatricians still commonly held false beliefs about fever and its management. 50% of the respondents recommended alternating antipyretics for instance. This generally mean giving acetaminophen and ibuprofen three hours apart, typically scheduling them until the child has recovered from the illness in order to prevent fever rather than just using them as fever occurs. Nearly a third of the pediatricians in the survey cited a nonexistent policy of the American Academy of Pediatrics as support of the practice. The AAP actually strongly recommends against such an approach to fever as it has not been shown to be more effective and it increases the likelihood of dosing errors.

Pediatricians tend to only discuss fever when children are sick, and when they do discuss it at well-child visits it usually involves warnings of when to seek medical care without education on the many commonly held false beliefs. Our emphasis of fever without accurately explaining what fever is leaves parents anxious and forces them to rely on alternative sources of information, such as the internet, which I’m told pretty much allows anybody to publish just about anything.

According to The Baby Adjustors,

If you child has a fever and acts abnormally, call your family chiropractor. Your child may be suffering from a spinal subluxation. This condition interferes with normal body function and can cause many childhood symptoms, including a fever.

Or your child may have meningitis that can progress to death in a matter of hours but that is just my Western medical bias. They don’t even explain what “acts abnormally” means. If your kid has a fever and is a Saints fan, he may have a subluxation. But this isn’t about how painfully bad and dangerous irregular medical advice can be, it is about how painfully bad and even sometimes dangerous real medical advice can be and how it can lead to parents and other caregivers treating benign childhood fever as a medical emergency.

Some have described fever as our friend. There is merit to the idea that fever has a beneficial purpose but it remains somewhat controversial. Elevating our core body temperature in response to infection is a primitive and almost universal response, seen even in cold-blooded species. Lizards have been observed staying in the sun longer and fish seeking out warmer water when ill for example. This implies at least that there is some degree of survival advantage in being able to develop a fever.

Some bacteria and viruses do grow poorly when exposed to higher temperatures. Iron is required for growth by many pathogenic bacteria, and it appears that fever decreases availability of it in the blood. Test tube studies have shown that elevated temperatures may increase the activity of various components of the immune system. There are a few non-primate experiments, particularly in rats and rabbits, that have shown improved outcomes with fever and even some human studies showing prolonged symptoms when fever is treated aggressively.

But everything seems to increase the activity of various components of the immune system in test tubes, and those studies were small and difficult to extrapolate to all humans or to all specific fever causing infections. Plus there is also data showing that the immune system may actually become impaired during high fevers above 104-105 degrees. And there is also evidence in animals and human patients that raises concerns of poorer outcomes from some illnesses, particularly in critically ill patients, with very high fever. It is a mixed picture essentially and the jury is still out. Regardless, any benefit of fever is likely so minimal that it would not preclude treatment of a miserable toddler with a temperature of 102.

Does this all mean that fever shouldn’t be taken seriously? Of course it doesn’t. In certain patient populations, fever requires immediate intervention. Very young or unimmunized children are at high risk for severe infections of the blood and brain. Febrile neonates and immune compromised patients, such as in Sickle Cell disease for just one of many examples, require laboratory investigation and even empiric antibiotic coverage even if they are completely well appearing. Prolonged and unexplained fever that lasts longer than a week, also justifies a work up. Fever is simply a clue, sometimes the only clue, that there is an infection going on. Thankfully in the vast majority of children, and I mean the vast majority, the infection is self-limited and viral.

Most pediatricians, emergency room doctors, nurse practitioners, and other medical professionals that care for children are well meaning folks who practice good medicine most of the time. But we are human and we are vulnerable to all of the weaknesses inherent in being human. Why are we so afraid of fever? Perhaps because of the biases, logical fallacies, and intellectual stumbling blocks that plague us all to varying degrees, particularly during such complicated endeavors as the practice of medicine. Or is it that we are simply parroting behaviors learned during impressionable years as medical learners.

Old habits are infamously hard to break in medicine. There will always be a subjective component to what I do, an art to the practice of medicine. But the science of medicine, preferably bolstered by the acquisition of good critical thinking skills, is necessary to recover from or avoid problems like fever phobia.


Posted by Clay Jones

Clay Jones, M.D. is a pediatrician and a regular contributor to the Science-Based Medicine blog. He primarily cares for healthy newborns and hospitalized children, and devotes his full time to educating pediatric residents and medical students. Dr. Jones first became aware of and interested in the incursion of pseudoscience into his chosen profession while completing his pediatric residency at Vanderbilt Children’s Hospital a decade ago. He has since focused his efforts on teaching the application of critical thinking and scientific skepticism to the practice of pediatric medicine. Dr. Jones has no conflicts of interest to disclose and no ties to the pharmaceutical industry. He can be found on Twitter as @SBMPediatrics and is the co-host of The Prism Podcast with fellow SBM contributor Grant Ritchey. The comments expressed by Dr. Jones are his own and do not represent the views or opinions of Newton-Wellesley Hospital or its administration.