What’s a “normal” human body temperature? That question is a little harder to answer than you might think.
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Most people probably grew up being told a body’s normal temperature was 98.6 degrees Fahrenheit (or 37 degrees Celsius). That widely accepted number originated from a study done in the mid-1800s.
So which is right? Well, the reality is there isn’t one exact “normal” body temperature, says family medicine physician Donald Ford, MD, MBA. Everyone has their own ordinary — and even that is more of a sliding scale than one set number.
Normal body temperature range
Your body temperature can move up and down and all around, but it usually stays within a certain window.
“Typically anything in the range of 97 to 99 degrees Fahrenheit is considered normal,” says Dr. Ford. “But there are times when a perfectly healthy person might have a body temperature that’s slightly higher or slightly lower than that.”
Your “normal” body temperatures changes throughout your life, too. It often rises from childhood into adulthood before dipping during the later years in life. By stages, it looks like this (with all temperatures for an oral reading).
- Infant to 10 years old: 95.9 F (35.5 C) to 99.5 F (37.5 C).
- Eleven to 65 years old: 97.6 F (36.4 C) to 99.6 F (37.6 C).
- Over 65 years old: 96.4 F (35.8 C) to 98.5 F (36.9 C).
Why does body temperature fluctuate?
A temperature check is usually part of a routine visit to your healthcare provider — and probably something you do at home if you’re not feeling well. Temperature is one of your vital signs, and it’s an important indicator of your health.
A healthy body, generally, is pretty good at keeping its temperature at a comfortable level: “For example, if you go outside on a very cold day, you will notice that your skin temperature is going to go down, but your core temperature inside will stay in the normal range,” explains Dr. Ford.
A part of your brain called the hypothalamus is responsible for this. When you get too cold, it signals your body to preserve heat by shrinking your blood vessels, and to produce heat by shivering. And when you get too hot, it signals your body to make sweat to cool off.
However, it’s normal for your temperature to change within a healthy range as you move through your day and your life.
Why is my temperature higher than normal?
A temperature that’s higher than 100.4 F (or 38 C) is considered a fever, and it’s usually something you should bring to your doctor’s attention, Dr. Ford says.
Oftentimes, a fever is your body’s reaction to an infection, like the flu. It doesn’t require any specific treatment, other than bringing your temperature down for comfort.
As for that gray area in between a fever and the high end of a healthy temperature? “We generally call this a ‘low-grade’ temperature,” Dr. Ford explains. “It’s certainly something to watch, but it’s hard to know the significance of this.”
Persistent low-grade or high-grade fevers could signal that something else is going on in your body. Several medical conditions, including hyperthyroidism and other endocrine disorders, can raise the body’s core temperature.
If your fever lasts for more than two days, it’s best to follow up with your doctor.
Take note: Fevers in kids
Young kids generally tend to push thermometer readings higher than adults. Their bodies haven’t yet mastered the art of regulating their body temperature, so they’re also more likely to spike fevers — and severe ones, at that.
“You may see a child that goes up to 103, 104, 105 degrees,” Dr. Ford says. “We recommend acetaminophen to try to prevent a rapid spike in temperature, which can induce some other problems.”
If your child’s fever does not come down with fever reducers, or if an infant younger than 3 months develops a fever, call your pediatrician.
Why is my body temperature low?
If your core body temperature dips down to 95 F (35 C) or lower, that’s considered hypothermia. It’s often caused by exposure to cold weather, but there are other factors that can put you at risk for hypothermia, such as age and certain medications.
Hypothermia is a medical emergency, so call 911 if you suspect you or someone else has hypothermia.
Is there a ‘best time’ to take your temperature?
There’s usually a reason why you head to the medicine cabinet to grab your thermometer: Someone in the house doesn’t feel well. Consider that the ideal time to take your temperature given the important health information the reading provides.
Know this, though: Body temperatures typically run a little lower in the morning and a bit higher in the afternoon. For women, it can also fluctuate depending on where you are in your menstrual cycle.
The takeaway on temperature
If you take your temperature with three different kinds of thermometers, you might get three different results. This isn’t necessarily cause for worry, Dr. Ford says.
“Testing an internal temperature is going to be more accurate than testing an external temperature,” he notes.
So a thermometer that goes under the tongue will likely give you a slightly higher but more accurate result than a forehead thermometer or one that goes under your armpit. (Those kinds may be an easier option to use with young kids, though.)
So next time you reach for your thermometer, remember that your normal isn’t necessarily going to be 98.6 F.
“Normal is a range, and people shouldn’t get worried if their temperature is varying a little bit within that range,” Dr. Ford says. “That doesn’t necessarily mean anything good, bad or otherwise.”
But if you have any questions or concerns about your temperature, don’t hesitate to call your primary care provider.