What Is Normal Body Temperature Range for Adults, Children, and Babies?

You’re not as hot as your ancestors.

The average body temperature has been falling for decades. it’s now below 98.6°F (37°C). What is normal body temperature today? The average body temperature is about 97.7°F (36.5°C).

If you’re concerned your body temperature is too high or low, remember that body temperature isn’t a single number, it’s a range. It varies for each person and it changes throughout the day and your life. Knowing your unique range can warn you about serious health problems.

In this article, you’ll learn the normal body temperature range, what is a fever and hypothermia, and how to take temperature accurately.

A picture of a woman holding a blue and white digital thermometer in her hands, headline "What Is Normal Body Temperature?"

What Is Normal Body Temperature?

Normal body temperature isn’t a single number, everyone has their own normal. Normal body temperature ranges from:

  • Adults: 97.7°F (36.5°C) to 99.5°F (37.5°C) (1)
  • Children: 97.52°F (36.4°C) (2)
  • Infants: 99.5°F (37.5°C) (3).

Body temperature varies depending on gender, time of day, activity level, food or fluid consumption, and the site measured. Or for women, the stage of the menstrual cycle.  

 

Is A temperature of 98.6 Normal?

In 1868, a German physician decided that 98.6°F (37°C) was the normal body temperature (4). He studied over a million temperatures of 25,000 people. But more recent studies have shown that normal body temperature is declining.

Researchers reviewed 27 newer body temperature studies and found that the average body temperature is below 98.6°F (5). And a recent study of 250,000 temperatures from 25,000 patients found that the average is 97.9° F.

Why is body temperature dropping? Body temperature adapts to your environment. Some ideas could be climate change, improving living standards, or changing diets (for example, more processed foods).

 

Why Does Body Temperature Change?

Your body temperature adapts constantly to your environment and its needs. Your core body temperature is regulated closely by a part of your brain called the hypothalamus (6). The hypothalamus compares your temperature to your normal temperature. 

If your temperature is too low, the hypothalamus signals your body to generate heat through shivering and preserving heat by restricting your blood vessels. When your temperature is too high, your hypothalamus signals your body to release heat by producing sweat to cool your skin.

 

How Does Age Affect Body Temperature?

As you age, your body is less adaptive to temperature changes (7).

Generally, children have higher body temperatures because they have a higher metabolism. 

Adults over 64 tend to have lower body temperature because they are less able to regulate body temperature. Because they lose their ability to regulate properly, they’re more prone to heat-related health problems. And it’s also harder for older people to conserve heat when it’s cold.

 

What Factors Affect Body Temperature?

It’s normal for your body temperature to change throughout the day and your life. Factors that affect your body temperature include:

  • Your age: body temperature tends to decrease as you get older
  • Being overweight can lower body temperature (8)
  • Cancer: People with cancer generally have higher body temperatures
  • Eating or drinking: eating generally raises body temperature after eating. But a cold drink may lower body temperature
  • Exercise: exercise raises body temperature, but your body temperature may fall below normal temporarily after exercise 
  • Location on the body that temperature is measured. Rectal temperatures are warmer than oral temperatures. Oral temperatures are warmer than auxiliary temperatures.
  • Hormones
  • A woman’s menstrual cycle
  • Showering: Generally, a hot shower or bath will raise body temperature and a cold shower will lower it
  • Time of day: body temperature rises during the day and lowers at night. It’s highest at 5 pm and lowest at 4 AM
  • Weather: cold weather lowers body temperature and hot weather raises body temperature
  • Wearing warm clothing or a blanket

 

What Is A Fever?

A fever (hyperthermia) means your temperature is higher than normal. Fever in itself isn’t usually a problem. A fever could mean that your body is fighting an infection. But a fever could be a sign of a more serious health problem. 

According to the CDC, a fever is a temperature of 100.4 °F (38 °C) or higher (9)

For children, a fever is generally above one of the following:(10)

  • A rectal temperature of 100.4°F (38°C)
  • An oral temperature of 99.5°F (37.5°C)
  • An axillary temperature of 99°F (37.2°C)

But a fever could mean a temperature that’s beyond your normal temperature range.

 

What Causes A Fever?

Generally, a fever means your body is fighting a bacteria or virus causing an infection. Other causes for fever include (11):

  • Antibiotics
  • Anti-seizure drugs
  • Autoimmune diseases
  • Blood pressure medications
  • Cancer
  • Heat exhaustion
  • Heatstroke

 

Besides a temperature higher than normal, fever symptoms include (12):

  • Loss of appetite
  • Chills 
  • Dehydration
  • Feeling weak
  • Headache
  • Irritability
  • Muscle aches
  • Shivering

 

When To See A Doctor For A Fever

If a fever is vital for fighting infections, should you let it do its job? Or should you try to shorten it? When to see a doctor depends on the person’s age, body temperature, symptoms, medical history, and the duration of the fever.

These recommendations are for people who are generally healthy. Recommendations may be different for people who are immunocompromised, undergoing chemotherapy, or had recent surgery.

 

When To See A Doctor For A Fever For Infants and Toddlers Chart

Age Temperature (taken rectally) When To See A Doctor
0-3 months 100.4 °F (38 °C) Call your doctor even if your child doesn’t have any other symptoms
3-6 months Up to 102 °F (38.9 °C) Call your doctor if your child is unusually irritable, tired, or uncomfortable
3-6 months Above 102 °F (38.9 °C) Call your doctor
6-24 months Above 102 °F (38.9 °C) Call your doctor if your child’s fever doesn’t respond to medication or lasts longer than a day

Source: Mayo Clinic (13

 

When To See A Doctor For A Fever For Children Chart

Age Temperature  When To See A Doctor
2-17 years Up to 102 °F (38.9 °C) taken rectally for children under 4 or taken orally for children over 3 Call your doctor even if your child appears unusually tired or complains of significant discomfort
2-17 years Above 102 °F (38.9 °C) taken rectally for children under 4 or taken orally for children over 3 Call your doctor if your child’s fever doesn’t respond to medication or lasts longer than 3 days

Source: Mayo Clinic (13)  

 

When To See A Doctor For A Fever For Adults Chart

Age Temperature (taken orally) When To See A Doctor
18 years and older Up to 102 °F (38.9 °C)  Call your doctor even if the person also has a severe headache, shortness of breath, a stiff neck, or other unusual symptoms.
18 years and older Above 102 °F (38.9 °C)  Call your doctor if the fever doesn’t respond to medication, stays at 103 °F (39.4 °C) or higher, or lasts longer than 3 days.

Source: Mayo Clinic (13

 

What Is Hypothermia?

Hypothermia is defined as a body temperature drop below 95°F (35 °C) (14) or a body temperature below normal. It’s caused by being in cold temperatures for a long time, Even a slightly cooler temperature can cause hypothermia for babies and older adults.

Untreated severe hypothermia can cause an irregular heartbeat, heart and respiratory failure, and death. Because hypothermia can make it difficult to think clearly and move properly, it makes it harder to get timely treatment.

 

What Are the  Symptoms of Hypothermia?

Early signs and symptoms of hypothermia include (15):

  • Cold skin
  • Confusion
  • Drowsiness
  • Loss of coordination
  • A weak pulse
  • Slow, shallow breathing
  • Shivering
  • Slurred speech
  • Weakness
  • For babies, cold, bright red skin

 

What Causes Hypothermia?

If you have hypothermia, your body is losing heat faster than it can generate it (16). Generally, hypothermia is caused by exposure to cold water, cold weather, or cold indoor temperatures. Hypothermia can be caused by the following situations (15):

  • Not wearing warm enough clothes for the weather conditions
  • Falling in water
  • Being unable to change out of wet clothes or get to a warmer, dry location
  • Staying in cold temperatures too long
  • Living in a home that’s too cold, either due to intense airconditioning or poor heating

Hypothermia is a serious concern for babies and the elderly who can’t regulate temperature properly. Some people can develop hypothermia in temperatures above 40°F or 4°C in certain situations, which include:

  • Being cold from sweating
  • Being in cold water for a long time
  • Being wet from the rain
  • Prolonged time spent in an airconditioned room

Hypothermia is a medical emergency. Call 911 If you suspect that you or someone else has hypothermia.

 

What’s The Best Location To Take Temperature?

The best location to take body temperature depends on the age and your need for accuracy or convenience.  Each site has its pros and cons.

Body temperature locations include:

  • Orally: You take an oral temperature by mouth with either a digital or a traditional glass thermometer. The oral temperature is both convenient and reliable.
  • Auxillary: You take auxiliary temperature under the armpit with either a glass or digital thermometer. Auxillary temperature is around 0.5 °F lower than the oral temperature Although taking auxiliary temperature is convenient, it’s less accurate.
  • Rectally. You take the rectal temperature in the bottom with a glass or digital thermometer. Generally, the rectal temperature is 0.5 °F higher than the oral temperature (17). Although this method is inconvenient, it’s considered the “gold standard” because it measures internal body temperature.  
  • Aural. You take the aural temperature in the ear with a special device to measure the temperature of the eardrum (17). Although the aural temperature is convenient, it’s not recommended because it’s less accurate.

 

Why Do Age and Fitness Level Affect Body Temperature?

Younger and fitter patients record wider temperature amplitudes (a wider range between the high and low temperatures) . But older and less fit patients recorded smaller amplitudes (a narrower range between high and low.

As a person ages, their body temperature generally decreases. And the ability of their body to adapt to different kinds of stressors decreases. Because of this, even subtle variations in core temperature can be significant for older patients. A fever in an older patient generally signifies a more severe infection that could be more life-threatening

 

Do This Before You Measure Body Temperature

Some activities affect body temperature temporarily. Wait until the patient’s body returns to normal for the most accurate results.

  • Wait about 30 minutes after eating or drinking a cold or hot drink, or smoking
  • Wait at least an hour after exercise or taking a hot shower or bath

 

Guidelines For Taking Temperature For Each Kind of Thermometer

Precautionary steps for taking temperature for each kind of thermometer are the following (18):

  • Follow the instructions that come with the thermometer
  • Clean the thermometer with rubbing alcohol or soap and warm water before and after each use
  • Use a different thermometer for oral and rectal temperatures, and label each one
  • Never leave a child alone while taking their temperature
  • Wait at least 6 hours after taking medications that lower body temperature

 

How To Take Oral Temperature 

For taking oral temperature, you’ll need a digital or a glass thermometer (without mercury). For taking oral temperature, follow these steps (18):

  1. Wait at least 30 minutes after eating or drinking
  2. Clean the thermometer before use
  3. For a glass thermometer, hold the opposite end of the bulb and shake the thermometer down until it reads 95°F or lower.
  4. Put the thermometer under the tongue, where it meets the lower jaw (the posterior subliminal pocket). This area gives the best reliability. 
  5. Make sure the mouth is closed and the lips are holding the thermometer in place
  6. For a glass thermometer, hold the thermometer in place for three minutes, 
  7. For a digital thermometer, wait for a beep
  8. Remove the thermometer and read and record the number

 

How To Take Rectal Temperature (for infants)

To take the rectal temperature of an infant, follow these steps from the Mayo Clinic (19)

  • Turn on the digital thermometer and lubricate the tip of the thermometer with petroleum jelly or another lubricate
  • Lay the child on his or her side or stomach with their knees flexed
  • Gently insert the tip of the thermometer 1/2 or 1 inch (1.3 to 2.5 centimeters into the rectum. Never force the thermometer through resistance.
  • Hold the child and the thermometer still until the thermometer beeps when it’s ready. Don’t let go of the thermometer when it’s inside the child to avoid injury
  • Remove the thermometer and read and record the number

A picture of a dark-haired young woman wearing a white bikini and a white hat looking up while holding her head, headline "What's normal body temperature | Why You're not as hot as your ancestors"

Do You Have A Hot Body Temperature?

You’re concerned that you or someone you love has a body temperature that’s too high or too low. 

Now you know the normal body temperature range. And you also learned how body temperature changes through the day and your lifetime. 

You’ve learned when to be concerned when your temperature is abnormal, and when you should seek medical help.

What’s your normal body temperature range? Knowing your normal could give you an early warning of serious health problems.

 

Further reading:

What Are the Vital Signs?

How To Get Rid of A cold Overnight

What Is A Good Resting Heart Rate?

What Is Normal Blood Pressure? | Blood Pressure Chart By Age

What’s the Normal Respiration Rate? | Respiration Rate Chart By Age

 

Sources Cited

  1. https://www.ncbi.nlm.nih.gov/books/NBK553213/
  2. https://www.nhs.uk/conditions/fever-in-children/
  3. https://www.ncbi.nlm.nih.gov/books/NBK279457/
  4. https://www.yalemedicine.org/news/temperature-checks-covid
  5. https://elifesciences.org/articles/49555
  6. https://www.ncbi.nlm.nih.gov/books/NBK279457/#:~:text=Our%20internal%20body%20temperature%20is,body%20generates%20and%20maintains%20heat.
  7. https://www.cdc.gov/aging/emergency-preparedness/older-adults-extreme-heat/
  8. https://www.nature.com/articles/s41366-018-0218-7
  9. https://www.cdc.gov/quarantine/air/reporting-deaths-illness/definitions-symptoms-reportable-illnesses.html
  10. https://www.pennmedicine.org/for-patients-and-visitors/patient-information/conditions-treated-a-to-z/fever
  11. https://medlineplus.gov/ency/article/003400.htm
  12. https://www.mayoclinic.org/diseases-conditions/fever/symptoms-causes/syc-20352759
  13. https://www.mayoclinic.org/diseases-conditions/fever/in-depth/fever/art-20050997
  14. https://www.hopkinsmedicine.org/health/conditions-and-diseases/hypothermia
  15. https://www.mayoclinic.org/diseases-conditions/hypothermia/symptoms-causes/syc-20352682
  16. https://my.clevelandclinic.org/health/articles/10881-vital-signs
  17. https://www.ncbi.nlm.nih.gov/books/NBK553213/#
  18. https://www.mayoclinic.org/how-to-take-temperature/art-20482578
  19. https://www.mayoclinic.org/healthy-lifestyle/infant-and-toddler-health/in-depth/thermometer/art-20047410

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