What’s a “normal” human body temperature? That question is a little harder to answer than you might think.
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.
But newer studies suggest the average person today actually runs a little cooler than that – somewhere between 97.5 F (36.4 C) and 97.9 F (36.6 C).
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?
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.
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.
Related Articles
You may have heard that the “normal” body temperature is 98.6°F (37°C). But this number is only an average. Your body temperature may be slightly higher or lower.
A body temperature reading above or below the average doesn’t automatically mean you’re sick. Several factors can influence your body temperature, including your age, sex, time of day, and activity level.
Read on to learn more about healthy body temperature ranges for babies, kids, adults, and older adults.
Your body’s ability to regulate temperature changes as you get older.
People over the age of 64 generally have more trouble adjusting to sudden changes in temperature as quickly as younger people. In general, older people have more difficulty conserving heat. They’re also more likely to have lower body temperatures.
Below are average body temperatures based on age, according to a review of studies and older research:
Identifying your normal range can make it easier to know when you have a fever.
Keep in mind that average body temperature varies from person to person. Your body temperature might be up to 1°F (0.6°C) higher or lower than the guidelines above.
There are four different ways to take your or a family member’s temperature. However, the reading can vary from one method to the next.
The chart below shows which method is recommended for each age group:
You may have had your temperature checked under your arm, in the armpit. This method isn’t as accurate and not recommended.
German doctor Carl Wunderlich identified the average body temperature of 98.6°F (37°C) during the 19th century. However, many studies have since determined that that isn’t always the case.
A 2019 study found that the average body temperature is 97.86°F (36.59°C). That’s a little lower than initially thought so many years ago.
However, it’s best to take this information with a grain of salt since no single number defines your average body temperature. Instead, it’s best to look at a temperature range that may be higher or lower than the average.
Here are some of the factors that affect body temperature:
- Our bodies tend to warm up throughout the day.
- Older adults have lower body temperatures since our ability to regulate body temperature lessens as we age.
- Younger people have higher body temperatures.
- The level of physical activity affects temperature because the more you move your body, the warmer your core body becomes.
- Hotter and colder weather can also mirror your body temperature — it rises when in a warm environment and lowers in the cold.
- Temperature readings from the armpit are lower than the thermometer read from the mouth.
- Thermometer readings from the mouth are lower than if taken in the ear or rectum.
- Hormone levels can affect body temperature.
- Excess weight can also be associated with lower body temperatures.
A higher-than-normal thermometer reading can be a sign of a fever.
The American College of Critical Care Medicine identifies a temperature of 100.9°F (38.3°C) or higher as a fever. As mentioned previously, the exact reading is dependent upon a few factors. If your temperature’s elevated above the normal range described earlier in the article, you may have a fever.
In general, a reading that’s 2°F (1.1°C) above your normal temperature is usually a sign of a fever.
Fevers can be accompanied by other signs and symptoms, including:
Our bodies have a built-in temperature control system. This operation raises the body temperature in response to disease and infection that you can sometimes fight without any intervention. With time and rest, your body temperature will likely return to normal without treatment.
With babies and younger children, it can be hard to know when to speak with a doctor. Call your pediatrician if:
- your baby is less than 3 months old and has a fever.
- your baby is between 3 months and 3 years old and has a temperature of 102°F (38.9°C).
- your child is 3 years or older and has a temperature of 103°F (39.4°C).
Seek medical care if your baby or child has a fever and:
- has difficulty breathing
- struggles to drink liquids
- is under 3 months old
- has a temperature over 104°F (40°C)
- is shivering for more than 30 minutes
- is inconsolable, especially when touched or moved
- is unable to move an arm or leg as normal
- appears dehydrated by low urine amounts, dry mouth, and no tears with crying
- has pain with urination
- appears very ill
If you feel your child should be seen by a medical professional, then trust your gut and have them checked out.
Hypothermia is a serious condition that occurs when you lose too much body heat. For adults, a body temperature that dips below 95°F (35°C) is a sign of hypothermia.
Most people associate hypothermia with being outside in cold weather for long periods of time. But hypothermia can occur indoors, too.
Babies and older adults are more susceptible. For babies, hypothermia can occur when their body temperature is 97°F (36.1°C) or lower.
Hypothermia can also be a concern in a poorly heated house in winter or an air-conditioned room in summer.
Other signs and symptoms of hypothermia include:
See a doctor if you have a low body temperature with any of the symptoms above.
A fever isn’t usually a cause for concern. The fever goes away with a few days of rest most of the time.
However, seek treatment when your fever climbs too high, lasts too long, or is accompanied by more severe symptoms.
Your doctor will ask questions about your symptoms. They might perform or order tests to determine the cause of the fever. Treating the cause of the fever can help your body temperature return to normal.
On the other hand, a low body temperature can also cause concern. Hypothermia can be life threatening if left untreated. Seek medical assistance as soon as you notice signs of hypothermia.
Your doctor will use a standard clinical thermometer to diagnose hypothermia and check for physical signs. In addition, they may use a low-reading rectal thermometer if needed.
In some cases, your doctor may order a blood test to confirm the cause of your hypothermia or to check for infection.
In mild cases, hypothermia may be harder to diagnose but easier to treat. Heated blankets and warm fluids can restore heat. Other treatments include blood rewarming and warmed intravenous fluids for more severe cases.
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