You may have heard that the “normal” body temperature is 98.6°F (37°C). This number is only an average. Your body temperature may be slightly higher or lower.
A body temperature reading that’s above or below the average doesn’t automatically mean you’re sick. A number of factors can influence your body temperature, including your age, sex, time of day, and activity level.
Read on to find out 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.
The average body temperatures based on age are estimated as:
- Babies and children. In babies and children, the average body temperature ranges from 97.9°F (36.6°C) to 99°F (37.2°C).
- Adults. Among adults, the average body temperature ranges from 97°F (36.1°C) to 99°F (37.2°C).
- Adults over age 65. In older adults, the average body temperature is lower than 98.6°F (36.2°C).
Keep in mind that normal 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. Identifying your own normal range can make it easier to know when you have a fever.
German doctor Carl Wunderlich identified the average body temperature of 98.6°F (37°C) during the 19th century. But in 1992, results from a study suggested abandoning this average in favor of a slightly lower average body temperature of 98.2°F (36.8°C).
The researchers pointed out that our bodies tend to warm throughout the day. As a result, a fever in the early morning might occur at a lower temperature than a fever that appears later on in the day.
Time of day isn’t the only factor that can influence temperature. As the ranges above indicate, younger people tend to have higher average body temperatures. This is because our ability to regulate body temperature decreases with age.
Physical activity levels and certain foods or drinks can also influence body temperature. Women’s body temperatures are influenced by hormones as well, and may rise or fall at different points during a woman’s menstrual cycle.
In addition, how you take your temperature can affect the reading. Armpit readings can be up to an entire degree lower than a reading from the mouth. And temperature readings from the mouth are often lower than readings from the ear or rectum.
A higher-than-normal thermometer reading can be a sign of a fever.
Among babies, children, and adults, the following thermometer readings are generally a sign of a fever:
- rectal or ear readings: 100.4°F (38°C) or higher
- mouth readings: 100°F (37.8°C) or higher
- armpit readings: 99°F (37.2°C) or higher
Research from 2000 suggests that fever thresholds for older adults might be lower, since older individuals have more difficulty conserving heat. In general, a reading that is 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:
- chills, shivering, or shaking
- hot or flushed skin
- body aches
- fatigue and weakness
- loss of appetite
- increased heart rate
Though a fever can leave you feeling pretty bad, it’s not dangerous. It’s simply a sign that your body is fighting something. Most of the time, rest is the best medicine.
However, you should call your doctor if:
- you have a temperature over 103°F (39.4°C)
- you’ve had a fever for more than three days straight
- your fever is accompanied by symptoms such as:
- chest pain
- a stiff neck
- a rash
- swelling in the throat
With babies and younger children, it can be hard to know when to call a doctor. You should seek medical care if:
- your baby is less than three months old and has a fever
- your baby is between three months and three years old and has a temperature of 102°F (38.9°C)
- your child is three years or older and has a temperature of 103°F (39.4°C)
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:
- slow, shallow breath
- slurred or mumbled speech
- a weak pulse
- poor coordination or clumsiness
- low energy or sleepiness
- confusion or memory loss
- loss of consciousness
- bright red skin that’s cold to the touch (in babies)
You should see a doctor if you have a low body temperature with any of the symptoms above.
A fever usually isn’t a cause for concern. Most of the time, a fever goes away with a few days of rest. However, when your fever climbs too high, lasts too long, or is accompanied by severe symptoms, you should seek treatment.
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 be cause for concern. Hypothermia can be life-threatening, if left untreated. It’s a medical emergency and you should seek medical assistance as soon as you notice signs of hypothermia.
Diagnosing hypothermia usually occurs based on someone’s physical signs and a standard clinical thermometer. A low-reading rectal thermometer may also be needed. A blood test may be used to confirm the cause of hypothermia or to look for infection.
In mild cases, it may be harder to diagnose, but easier to treat. Heated blankets and warm fluids can be used to restore heat. For more severe cases, other treatments include blood rewarming and using warmed intravenous fluids.