When you’re feeling sick and wondering whether to go to work or school, the thermometer often has the final verdict. Most people have been taught a body temperature of 98.6 Fahrenheit is normal, while 100.4 or above indicates a fever.
But a TikTok user recently went viral when she said her normal body temperature was about a degree lower, at 97.6, and she felt horrible at 99.1.
“It’s elevated but it’s not considered a temperature,” said the woman, who recorded herself while sounding congested, lying in bed, covered by blankets and apparently sick.
“I just know I don’t feel good.”
The video prompted hundreds of comments, with many people complaining their illnesses are not taken seriously if they don’t have a conventional fever.
“I always feel guilty for feeling utterly wrecked when I’m at 99°,” one commenter wrote.
“The nurse at school wouldn’t believe me because I ‘didn’t have a fever.’ I would be so sick and forced to finish the day,” another added.
Doctors say it’s completely valid to feel unwell even if you don’t have a high temperature.
If you feel sick, you are sick, says Dr. Julie Parsonnet, an infectious diseases clinician and professor of medicine at Stanford University, whose research includes studies on human body temperature.
The “normal” body temperature of 98.6 Fahrenheit is outdated, she adds, and relying on a number to define a fever is misplaced.
“If you are feeling really crummy and you have body aches and headaches and a sore throat, you’re sick — regardless of what your temperature is,” Parsonnet tells TODAY.com.
“If you don’t have a temperature, it doesn’t mean you’re not sick.And it doesn’t mean you should go to school. It doesn’t mean you should go to work.”
How was normal body temperature determined?
In the 1850s, German physician Carl Reinhold August Wunderlich took temperatures from 25,000 patients and calculated the average body temperature to be 37 degrees Celsius, or 98.6 Fahrenheit.
Researchers call him “the father of clinical thermometry.”
“That’s where we got that number from,” Parsonnet says. “(But) it’s outdated because physiologically, we’ve changed. We are much healthier, we’re taller, we’re fatter and we’re colder than we were in the 1850s.”
In the middle of the 19th century, when Wunderlich calculated the average body temperature, life expectancy was 40 and many people had tuberculosis, dental disease, rheumatic heart disease and all sorts of chronic infections that might have led them to have a higher body temperature compared to today, she notes.
Modern humans have less chronic inflammation thanks to medicine and higher standards of living, and they spend more time in “thermoneutral zones” — heated or air-conditioned places where it’s not too cold or too hot. Those are two of the possible reasons why human body temperature has been decreasing over the last 150 years, Parsonnet and her colleagues wrote in a study analyzing the change.
What is the normal body temperature?
The average normal oral body temperature is now 97.9 degrees Fahrenheit, though it can range from 97.2 to 98.3 Fahrenheit, a separate study of hundreds of thousands of people found.
The previous standard of 98.6 Fahrenheit “needs to be retired,” Parsonnet and her colleagues wrote in the paper.
But there is no absolute perfect temperature that fits everybody, she says. It depends on sex, age and other factors, such as time of day.
It’s usually highest in the evening and can be influenced by exercise, strong emotion, room temperature and a woman’s menstrual cycle, according to the National Library of Medicine. Even the gut microbiome has an impact, researchers say.
You can use an online tool from Stanford University to figure out your personal body temperature.
What is considered a fever?
An oral temperature above 99 degrees Fahrenheit for an adult and 99.5 for a child is probably a fever, the National Library of Medicine notes. But people shouldn't be hung up on a number, experts say.
“When you start getting up to levels 99 to 100, everybody would say that’s abnormal,” Parsonnet says.
“But if you’re an elderly person, you’ll never get there. To them, a temperature of 98.6 might, in fact, be really abnormal.”
Older adults generally have a lower body temperature compared to younger people, she notes. Her elderly mother-in-law had a heart infection, but never had a conventional fever so she was sick for a month before being diagnosed.
“So you can be quite sick and have a normal temperature. You can be quite sick and have a low temperature. You just have to pay attention to the bigger picture of what’s going on in this human being and not rely so much on that number,” Parsonnet says.
“I think a lot of us have grown up with our parents saying, ‘If your temperature is normal, you’re going to school, you’re not really sick.’ That’s not true.”
