What is a normal body temperature?

So you thought you knew what a normal body temperature is? Not so fast. Did you know that a normal body temperature depends on many factors, including:

• a person’s age,
• sex (male/female)
• activity levels
• for women whether they are pregnant or not
• for non-pregnant women in which menstrual cycle stage they are: if they are before or after ovulation
• body mass index
• the time of the day, typically being lowest in the early morning and highest in the late afternoon
• food and fluid intake
• the method of measurement, such as highest rectal (bottom), then oral (mouth), ear, and lowest armpit readings
• ethnicity

For many but not all people an average human body temperature is 98.6 °F (37 °C) orally. The normal range can be as low as 97.5 °F and as high as 98.8 °F (36.4 °C to 37.1 °C). The body temperature is considered dangerously low when it's below 95 F (35 C). There are some people with average temperatures in the 96 F range who are fine

Rectal temperatures:

0–2 years: 97.9–100.4°F (36.6–38°C)
3–10 years: 97.9–100.4°F (36.6–38°C)
11–65 years: 98.6–100.6°F (37.0–38.1°C)
Over 65 years:  97.1–99.2°F (36.2–37.3°C)

Ear temperatures:

0–2 years: 97.5–100.4°F (36.4–38°C)
3–10 years: 97.0–100.0°F (36.1–37.8°C)
11–65 years: 96.6–99.7°F (35.9–37.6°C)
Over 65 years: 96.4–99.5°F (35.8–37.5°C)

Oral temperatures:

0–2 years: 95.9–99.5°F (35.5–37.5°C)
3–10 years: 95.9–99.5°F (35.5–37.5°C)
11–65 years: 97.6–99.6°F (36.4–37.6°C)
Over 65 years: 96.4–98.5°F (35.8–36.9°C)

Armpit temperatures:

0–2 years: 94.5–99.1°F (34.7–37.3°C)
3–10 years: 96.6–98.0°F (35.9–36.7°C)
11–65 years: 95.3–98.4°F (35.2–36.9°C)
Over 65 years: 96.0–97.4°F (35.6–36.3°C)

Download this helpful graphic from Welch-Allyn

What is an elevated temperature? 

In adults, the following temperatures suggest that someone has a fever:

• at least 100.4°F (38°C) is a fever
• above 103.1°F (39.5°C) is a high fever
• above 105.8°F (41°C) is a very high fever

Researchers have looked into the individual differences between people’s normal body temperatures. A study looking at almost 35,500 people found that older adults had the lowest temperatures, and African-American women had higher temperatures than white men.
They also found that certain medical conditions can affect a person’s body temperature. For example, people with an underactive thyroid (hypothyroidism) tended to have lower temperatures, while people with cancer had higher temperatures. 

Google search "What is fever?"

On December 27, 2020 babyMed conducted an incognito Google search for "What is fever?". Here are the top 20 URLs and definitions:

Search incognito window: What is fever?

1. "Newer research suggests that the number has since gone down. In a recent review, scientists looked at temperature records from three periods between 1860 and 2017. The average oral temperature slowly fell by about 1 degree to 97.5 F. A person’s age, gender, or weight didn’t make a difference, nor did the time of day."
"doctors don’t consider you to have a fever until your temperature is at or above 100.4 F" and "Anything above 100.4°F is considered a fever. " https://www.webmd.com/lung/what-is-a-fever#1

2. "You have a fever when your temperature rises above its normal range. What's normal for you may be a little higher or lower than the average normal temperature of 98.6 F (37 C)"
"Although most people consider 98.6 F (37 C) normal, your body temperature can vary by a degree or more — from about 97 F (36.1 C) to 99 F (37.2 C) — and still be considered normal."
https://www.mayoclinic.org/diseases-conditions/fever/symptoms-causes/syc-20352759

3. "A person has a fever if their body temperature rises above the normal range of 98–100°F (36–37°C). It is a common sign of an infection."
https://www.medicalnewstoday.com/articles/168266#_noHeaderPrefixedContent

4. "Temperature in the anus (rectum/rectal) is at or over 37.5–38.3 °C (99.5–100.9 °F) An ear (tympanic) or forehead (temporal) temperature may also be used.
Temperature in the mouth (oral) is at or over 37.2 °C (99.0 °F) in the morning or over 37.7 °C (99.9 °F) in the afternoon
Temperature under the arm (axillary) is at or over 37.2 °C (99.0 °F) https://en.wikipedia.org/wiki/Fever

5. "Although a fever (pyrexia) could be considered any body temperature above the normal temperature of 98.6 degrees Fahrenheit (98.6 F or 37 C), medically, a person is not considered to have a significant fever until the temperature is above 100.4 F (38.0 C)." https://www.medicinenet.com/aches_pain_fever/article.htm

6. "In general, a baby has a fever when their body temperature exceeds 100.4°F (38°C). A child has a fever when their temperature exceeds 99.5°F (37.5°C). An adult has a fever when their temperature exceeds 99–99.5°F (37.2–37.5°C)."
https://www.healthline.com/health/fever#what-to-look-for

7. "It’s normal for your body temperature to fluctuate throughout the day. But in general, if you’re an adult and your temperature is above 100.4°F (38°C), you have a fever." https://www.healthline.com/health/how-to-tell-if-you-have-a-fever#Symptoms-to-watch-for

8. "A fever is a body temperature that is higher than normal. A normal temperature can vary from person to person, but it is usually around 98.6 °F (37 °C). A fever is not a disease. It is usually a sign that your body is trying to fight an illness or infection." https://medlineplus.gov/fever.html

9. "The medical community generally defines a fever as a body temperature above 100.4 degrees Fahrenheit. A body temp between 100.4 and 102.2 degree is usually considered a low-grade fever." https://www.osfhealthcare.org/blog/whats-considered-a-fever-and-when-to-see-a-doctor/

10. "An adult probably has a fever when the temperature is above 99°F to 99.5°F (37.2°C to 37.5°C), depending on the time of day." https://www.pennmedicine.org/for-patients-and-visitors/patient-information/conditions-treated-a-to-z/fever

11, "Some experts define a low-grade fever as a temperature that falls between 99.5°F (37.5°C) and 100.3°F (38.3°C)." https://vicks.com/en-us/treatments/how-to-treat-the-flu/what-low-grade-fever

12. "Under normal conditions, the temperature of deeper portions of the head and trunk does not vary by more than 1–2 °F in a day, and it does not exceed 99 °F (37.22 °C) in the mouth or 99.6 °F (37.55 °C) in the rectum. Fever can be defined as any elevation of body temperature above the normal level. "
https://www.britannica.com/science/fever

13. "Your normal body temperature is approximately 37C. A fever is usually when your body temperature is 37.8C or higher. " https://www.nhsinform.scot/illnesses-and-conditions/infections-and-poisoning/fever-in-adults

14. "CDC considers a person to have a fever when he or she has a measured temperature of 100.4° F (38° C) or greater, or feels warm to the touch, or gives a history of feeling feverish." https://www.cdc.gov/quarantine/air/reporting-deaths-illness/definitions-symptoms-reportable-illnesses.html

15. "Normal body temperature ranges from 97.5°F to 98.9°F (36.4°C to 37.2°C). It tends to be lower in the morning and higher in the evening. Most healthcare providers consider a fever to be 100.4°F (38°C) or higher. "
https://www.hopkinsmedicine.org/health/conditions-and-diseases/fever

16. "A fever is a higher-than-normal body temperature. " "For adults, a fever is when your temperature is higher than 100.4°F."
"For kids, a fever is when their temperature is higher than 100.4°F (measured rectally); 99.5°F (measured orally); or 99°F (measured under the arm)."
https://my.clevelandclinic.org/health/symptoms/10880-fever

17. " A low-grade fever below 100.4 degrees Fahrenheit is usually not problematic, but if your body temperature is higher than 100.4 degrees Fahrenheit, this is considered a high-grade fever and you need to talk to your doctor about it." https://www.verywellhealth.com/what-is-a-fever-770340

18. "Most healthcare providers consider a fever to be 100.4°F (38°C) or higher. A person with a temperature of 99.6°F to 100.3°F has a low-grade fever." https://www.cedars-sinai.org/health-library/diseases-and-conditions/f/fever.html

19. "When you have a fever, your body temperature rises above 37.5C (99.5F). This usually means there is something wrong somewhere." https://www.cancerresearchuk.org/about-cancer/coping/physically/fever/what-is-fever

20. "Most centres define fever as body temperature higher than 38°C. Temperatures between 37.5°C and 38.5°C may indicate a low-grade fever. A high-grade fever is present when the oral temperature is above 38.5°C."
https://www.mydr.com.au/kids-teens-health/fever

21. "Since body temperature rarely climbs above 99.9 degrees without a reason, this guide will consider a fever to be present when the body temperature is 100.0 F (38 degrees C) or higher."
https://www.health.harvard.edu/decision_guide/fever-in-adults

Reasons for a low temperature

The most common cause of a lower-than-normal body temperature is exposure to cold. But occasionally, low body temperature can indicate an underlying problem or condition, such as:

• Inactivity
• Underactive thyroid (hypothyroidism)
• Diabetes
• Adrenal gland insufficiency (Addison's disease)
• Hypothalamus dysfunction
• Liver failure
• Kidney failure
• Widespread infection (sepsis)
• Excessive use of alcohol or illicit drugs
• A side effect of certain medications, such as phenothiazines, barbiturates, opiates, clonidine, lithium, and benzodiazepines
• Cold exposure
• Alcohol consumption (see Alcohol use)
• Hypoglycemia
• Impaired shivering capacity in elderly
• Myxoedema
• Starvation
• Malnutrition
• Hypopituitarism
• Exposure to cold outdoors
• Immersion in cold water
• Vasoconstriction failure
• Kwashiorkor
• Erythroderma
• Paget's disease of bone
• Uremia
• Cerebrovascular injury (see Cerebrovascular symptoms)
• Cerebral trauma
• Diabetic ketoacidosis
• Wernicke's encephalopathy
• Carbon monoxide poisoning
• Anoxic brain injury
• Cardiac arrest
• Organophosphate poisoning
• Spinal cord lesion
• Terminal malignant disease
• Severe hepatic cirrhosis