Body Temperature: What Is (and Isn’t) Normal?

Your temperature fluctuates throughout your day — and your life
checking temperature with a digital thermometer

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 it was 98.6 degrees Fahrenheit (or 37 degrees Celsius). That widely accepted number originated from a study done in the mid-1800s. But newer studies suggest the average person today actually runs a little cooler than that – somewhere between 97.5 F and 97.9 F

The reality is, there isn’t one exact “normal” body temperature, says family medicine physician Donald Ford, MD, MBA. Everyone has their own normal —and it’s more of a sliding scale than one set number. 

“We’re cautious about saying what a normal temperature is, because the truth is there’s a whole range of them,” he says.

“Typically anything in the range of 97 to 99 degrees Fahrenheit is considered normal, but there are times when a perfectly healthy person might have a body temperature that’s slightly higher or slightly lower than that.”

Keep the following in mind the next time you take your temperature.

Your body’s thermostat

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, Dr. Ford says. 

“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,” he explains.

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 the blood vessels, and to produce heat by shivering. And when you get too hot, it signals your body to make sweat to cool off. 

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However, it’s normal for your temperature to change within that healthy range as you move through your day and your life. For example, your temperature is usually lower in the morning than it is in the afternoon. For women, it can also fluctuate depending on where you are in your menstrual cycle. 

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, and 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. A number of medical conditions, including hyperthyroidism and other endocrine disorders, can heighten the body’s core temperature, so if your fever lasts for more than two days, follow up with your doctor.

Take note: Kids’ fevers

Young kids generally tend to run warmer 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?

Studies show that core body temperature decreases with age. Hypothyroidism, or an underactive thyroid, can also slow down metabolism, which can lead to a drop in body temperature.

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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.

The takeaway on your 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 one that goes under your armpit, or a forehead thermometer — though these kinds may be an easier option to use with kids.

So next time you reach for your thermometer, remember that your normal isn’t necessarily going to be 98.6 degrees 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.

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