Is 99.9 a Fever?

Reviewed on 6/22/2021

Normal temperatures can vary throughout the day (lower temperatures in the early morning and higher temperatures in the late afternoon). A temperature of 99.9° F (in the armpit) would be considered a fever only in babies under one year. A core (rectal) body temperature of 100.4° F (38.0° C) or higher in adults, and 99° F (37.2° C) (armpit) or 100.4° F (38° C) (rectal) in babies under one year is considered a fever.
Normal temperatures can vary throughout the day (lower temperatures in the early morning and higher temperatures in the late afternoon). A temperature of 99.9° F (in the armpit) would be considered a fever only in babies under one year. A core (rectal) body temperature of 100.4° F (38.0° C) or higher in adults, and 99° F (37.2° C) (armpit) or 100.4° F (38° C) (rectal) in babies under one year is considered a fever.

A fever is a higher-than-normal body temperature, which is not an illness in itself, but a symptom that often occurs when the body is fighting an infection.

The standard of 98.6° F (37° C) as a normal average oral temperature was established in the 1800s but recent studies have shown the average body temperature has dropped to 97.5° F (36.4° C). It is believed this is due to a combination of more accurate thermometers, lower rates of infection, and lower metabolic rates because people weigh more on average today than they did in the 1800s. 

Normal temperatures can vary throughout the day, with lower temperatures occurring in the early morning and higher temperatures in the late afternoon, sometimes reaching 99.9° F (37.7° C) in adults. 

Technically, 99.9° F would be considered a fever only in babies under one year and only when measured axially (in the armpit), but not in adults. A core (rectal) body temperature of 100.4° F (38.0° C) or higher in adults, and 99° F (37.2° C) (armpit) or 100.4° F (38° C) (rectal) in babies under one year is considered a fever. 

A fever isn't usually a concern unless it reaches 103° F (39.4° C) or higher. 

Contact your doctor if you have a fever that: 

Seek medical attention right away if you have symptoms that accompany a fever such as:

What Causes Fever?

Fever may be caused by:

What Is the Treatment for Fever?

The goal of treatment for a mild fever is to relieve symptoms, and may include: 

  • Drinking fluids to stay hydrated
  • Resting
  • Use of over-the-counter (OTC) fever reducers such as acetaminophen (Tylenol or ibuprofen (Advil, Motrin)
    • Do not give aspirin to children because it may trigger Reye's syndrome, a rare but potentially life-threatening disorder 
  • Antibiotics 
    • For fevers caused by bacterial infections
    • Antibiotics are not used to treat infections caused by viruses

Infants may need to be admitted to a hospital for treatment for a fever because it may be a sign of a serious infection that requires intravenous (IV) medications.

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Reviewed on 6/22/2021
References
https://elifesciences.org/articles/49555

https://www.merckmanuals.com/professional/pediatrics/symptoms-in-infants-and-children/fever-in-infants-and-children

https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Education/Fact-Sheets/Febrile-Seizures-Fact-Sheet

https://www.merckmanuals.com/home/infections/biology-of-infectious-disease/fever-in-adults#:~:text=Fever%20is%20an%20elevated%20body,by%20a%20rectal%20thermometer.