If you’ve found yourself puzzling over your thermometer and wondering what temperature is considered a fever lately, you’re definitely not alone. Given that fever is the most common symptom of the new coronavirus, it’s understandable if you’ve been taking your temperature at every sign of ache, pain, or sniffle. But before you get scared if your thermometer reads a bit higher than 98.6, you should understand a few things about what temperature is considered a fever, and what actually warrants concern.
The first thing you should understand is that not everyone who has COVID-19 gets a fever, but it’s the most common symptom of confirmed cases, according to a report from China by the World Health Organization. According to the report, which was based on 55,924 confirmed cases as of February 20, 2020, the typical signs of COVID-19 included: “fever (87.9%), dry cough (67.7%), fatigue (38.1%), sputum production (33.4%), shortness of breath (18.6%), sore throat (13.9%), headache (13.6%), myalgia or arthralgia (14.8%), chills (11.4%), nausea or vomiting (5.0%), nasal congestion (4.8%), diarrhea (3.7%), and hemoptysis (0.9%), and conjunctival congestion (0.8%).” The fact that nearly 90% of people with confirmed cases had a fever explains why some countries are instituting fever checks at airports to try to screen out sick passengers. That said, it’s important to note that not all confirmed cases of COVID-19 include a fever, and also that people with no symptoms at all can also test positive—so the absence of a fever doesn’t necessarily mean that you’re in the clear. We’ll get to that in a bit.
First, though, back to you, taking your temperature, staring at your thermometer in concern. If you feel like crap but your thermometer swears you don’t have a temperature, where does that leave you? Or if you feel generally okay but you’re reading a temperature higher than 98.6, what should you do? Well, it turns out that diagnosing a fever may not be as straightforward as we’ve been led to believe. Here are a few common questions you might have about fevers, taking your temperature, and assessing your health, as well as answers from doctors.
What temperature is considered a fever?
Technically, the CDC defines a fever as having a temperature of 100.4 degrees or greater. However, the organization says that it also considers someone to have a fever when they “feel warm to the touch or give a history of feeling feverish.”
The Infectious Diseases Society of America also recognizes that fever detection isn’t totally clear-cut. The organization says you have a fever if you have a single oral temperature of more than 100 degrees Fahrenheit or two repeated oral temperatures above 99 degrees, a rectal temperature above 99.5 degrees, or an increase in your temperature of two degrees over your baseline.
“If a temperature exceeds an upper limit of 100 degrees, I consider it abnormal,” Morton Tavel, M.D., a clinical professor of medicine at the Indiana University School of Medicine and author of Snake Oil Is Alive and Well: The Clash Between Myths and Reality—Reflections of a Physician, tells SELF.
Basically, there’s a lot of room for interpretation and context here.
Why do we consider 98.6 degrees a normal temperature?
We’ve been trained to think of 98.6 degrees as a “normal” temperature, but it’s actually just an average, Susan Besser, M.D., a primary care physician at Mercy Medical Center in Baltimore, tells SELF.
Yep, it turns out that oft-cited number originally came from the work of German doctor Carl Wunderlich in the 1800s. Subsequent modern studies have disagreed on the exact average number (such as this 1992 study in JAMA that settled on 98.2 degrees). And new research published in January 2020 suggested that the new average temperature is actually 97.9 degrees.
So, although 98.6 degrees may be a fine estimate of “normal” for many people, your personal normal temperature may be a bit higher or lower, as long as you still feel okay. “Few people have 98.6 as their normal, really,” Dr. Besser says.
Why does my temperature change throughout the day?
Glad you asked. This introduces another confusing problem: Your baseline temperature can vary based on several different factors.
Your temp is going to vary based on the time of day and what you’re doing, Dr. Besser says. In general, your baseline temperature is lower in the morning, revs up during the day, and goes down overnight because your metabolism is slower while you sleep.
Aside from that, there are a bunch of other things that can affect your body temperature. That includes your age, drinking alcohol, physical activity, being severely dehydrated, and where you are in your menstrual cycle.
Also worth noting that if you’re concerned about the new coronavirus, people report fevers (and other symptoms) that can come and go. Doctors recommend that, if you’re worried you have the new coronavirus, you take your temperature twice per day for several days in a row, and make sure that at least one of those times is during the afternoon or evening hours when the temperature might be naturally higher.
How can I figure out my normal, or baseline, temperature?
If you want to try to figure out your standard baseline temperature, you can try taking it for a few days in a row at the same time when you’re healthy, Dr. Tavel says. That should give you a pretty decent idea, but you have to make sure you’re consistent about it.
Another important thing to remember is that whenever you’re taking your temperature, make sure you’re doing it correctly.
First off, your choice of thermometer matters: If you take your temperature with a forehead thermometer, you’re probably going to get a slightly different number than if you used an ear, oral, or rectal thermometer. Rectal thermometers are the best way to get an accurate temperature, Dr. Besser says, but you’re probably not in a huge rush to get one of those.
When using an oral thermometer, you also want to make sure that you’re keeping your mouth closed the entire time, she says. Keep in mind that if you keep opening your mouth because you’re coughing or congested, it’ll make your reading less accurate.
What other symptoms besides fever should I worry about or pay attention to?
A fever is just one symptom and the way you feel matters just as much as your temperature.
“A fever or higher temperature does tell you that there’s inflammation, either from an infection or some other inflammatory process,” Russ Kino, M.D., medical director of the Weingart Foundation Emergency Department at Providence Saint John’s Health Center in Santa Monica, California, tells SELF. “[But] you don’t need to have a fever to be sick.” For example, as the CDC explains, a fever is a common symptom of the flu and rarely a symptom of the common cold—but it’s possible to have a fever (or not have one) with either illness. So, although a fever may be an important clue, it’s still just one piece of the puzzle.
This brings us back to the new coronavirus. If you’re experiencing symptoms of COVID-19—such as fever or a cough—it’s possible you might have it, according to the Centers for Disease Control. In that case, try to stay calm—many people can have mild versions of the disease and can recover at home (in fact, if your symptoms are mild it’s really important that you stay home, rather than go to the E.R. so that we don’t risk overloading our already overburdened health care system). The first thing you should do if you develop symptoms is to contact your healthcare provider to discuss how you’re feeling. Follow your doctor’s instructions about what to do to take care of yourself and minimize the potential that you’ll infect others. If your symptoms remain mild, you can recover at home by getting lots of rest, hydrating, practicing good hand hygiene and self-isolation, and managing your fever or aches and pains with an over-the-counter medication like acetaminophen. You can see all the CDC’s advice for what to do when you’re sick with a suspected case of COVID-19 here.
That said, you should also be aware of what symptoms to look out for that signal that the disease has gotten worse and that you might need emergency medical attention. Emergency warning signs include trouble breathing, persistent pain or pressure in your chest, feeling confused or unable to rouse, or bluish lips or face. If you experience these symptoms, call your doctor—or 911—immediately. Here’s some more information about when to know if you should go to the emergency room with a suspected case of COVID-19.
When should I worry about a fever that isn’t from the coronavirus?
COVID-19 isn’t the only disease that causes fevers! Colds, the flu, bacterial infections, and other diseases can cause fevers. In the case of a cold or flu, if the symptoms are mild, you can probably ride it out at home. But if you have a fever (over 100.4) and other worrying symptoms, such as difficulty breathing, pain when you urinate, or other concerning symptoms that could suggest an infection, you should call your doctor. The same goes for if you’ve been dealing with a fever for two days and over-the-counter meds don’t seem to be helping.
And if your fever really gets up there (above 103), that’s definitely a cause for concern and a sign that you need medical attention—call your doctor then too. And, of course, if any symptoms you have are severe—whether you have a fever or not—it’s important to check in with your doctor to figure out what’s going on.
Editor’s Note: This story was originally published on February 14, 2018, and was updated on March 30, 2020, to reflect more recent events and information about the new coronavirus.