Recently, I heard the suggestion that if someone has a fever, "get him or her warm enough to sweat it out." This recommendation is presumably based on the idea that fever is good for you and actually helps rid you of the disease (usually an infection) that's causing the fever. I also grew up with this advice: "Feed a cold, starve a fever." Are these recommendations worthwhile or are they based on myth?
The human body maintains a fairly steady temperature (around 98.2 degrees Fahrenheit) because a part of the brain (the thermoregulatory center of the hypothalamus) acts as a thermostat. It detects changes in body temperature and sends signals to the rest of the body to keep it in this narrow range. For example, it may tell blood vessels to constrict (to conserve heat) or to dilate (to get rid of heat). It may surprise you to learn that the body's thermostat is programmed to vary body temperature over the course of the day, lower in the early morning (around 97.5 degrees), higher around 4PM (up to 98.9 degrees). And there is variability among normal people: About 1% of the normal population has a temperature as high as 99.9 degrees in the afternoon. Fever develops when the body's thermostat is reset at a higher temperature, most commonly because of an infection.
Even when you aren't sick, body temperature can rise slightly above what would be considered normal. For example, it rises a bit just after a meal or during exercise. In addition, women have a lower morning temperature for the two weeks before ovulation and a 1-degree rise after ovulation until menstruation begins. This can help women to determine when ovulation is occurring, something that may be helpful to know when trying to become pregnant. Body temperature also depends on how it is measured: Rectal temperature is about 1 degree higher than that measured orally.
What Is a Fever?
Fever is an elevation in body temperature above normal and is most commonly due to an infection. However, there are many non-infectious causes of fever, including medications or vaccinations, some cancers, rheumatic diseases (such as lupus) and an overactive thyroid.
Perfectly healthy people can develop fever in an environment where the body can't get rid of heat well. For example, if you exercise on a hot day, your body temperature can rise to dangerous levels; the deaths of athletes preparing for the upcoming football season are examples of this. Since sweating is an important way for the body to remove heat, dehydration, humidity and extra clothing increase the risk.
Is Fever Bad for You?
Fever itself is usually harmless — the disease causing a fever is usually more important to identify and treat than is the fever itself — but there are situations where fever can cause trouble of its own. For example, elevations in body temperature make the heart and lungs work harder; for those with significant disease in those organs already, a high fever can be dangerous. Children who have had febrile seizures in the past are at a higher risk for another seizure if they have a fever.
Although less dangerous, fever often is accompanied by headache, muscle aches, fatigue and dehydration. In some situations, these symptoms are worse than the disease causing the fever in the first place, and efforts to reduce the temperature help to decrease these troublesome symptoms.
Is Fever Good for You?
Fever does serve some important, and potentially useful purposes:
For the most common disorders associated with fever, however, there's no convincing evidence that fever itself hastens recovery from common infections or that it correlates with a better outcome. There's experimental evidence that higher temperatures are harmful to certain bacteria, but medical experts disagree about whether this translates into a role for fever improving our ability to fight infection. In fact, most experts do agree that suppressing fever (for example, with acetaminophen) is not harmful, may be helpful, and they would never suggest trying to raise body temperature when fever is present.
Starve a Fever?
Many people who have a fever feel unwell and their appetite may be poor. This observation may have led to the idea that one should "starve a fever." In fact, there is no evidence that such a plan is helpful, and, again, it could even be harmful. People who have poor nutrition already may become even sicker if they try to "starve a fever." Drinking plenty of fluids should be a priority, since fever promotes fluid loss from the body and dehydration is a recognized risk.
The Bottom Line
Maintaining normal body temperature is important; fortunately, the human body generally takes care of this automatically and tolerates mild elevations well. Since higher body temperature doesn't contribute to recovery, efforts to raise body temperature during a fever aren't advisable and may even be dangerous. And while one's appetite may be poor when a fever accompanies illness, there's no clear benefit (and there may be harm) to the strategy of trying to "starve a fever."
Robert H. Shmerling, M.D. is associate physician at Beth Israel Deaconess Medical Center and associate professor at Harvard Medical School. He has been a practicing rheumatologist for over 20 years at Beth Israel Deaconess Medical Center. He is an active teacher in the Internal Medicine Residency Program, serving as the Robinson Firm Chief. He is also a teacher in the Rheumatology Fellowship Program.