Normal body temperatures vary depending on many factors, including a person’s age, sex, and activity levels. The normal body temperature for an adult is around 98.6°F (37°C), but every person’s baseline body temperature is slightly different, and may consistently be a little higher or lower. Your body’s ability to regulate temperature changes as you get older. In general, older people have more difficulty conserving heat. They’re also more likely to have lower body temperatures.

Normal body temperature

Most people think a normal body temperature is an oral temperature (by mouth) of 37°C (98.6°F). This is an average of normal body temperatures. Your normal body temperature may actually be 0.6°C (1°F) or more above or below this. Also, your normal temperature changes by as much as 0.6°C (1°F) during the day, depending on how active you are and the time of day. Body temperature is very sensitive to hormone levels. So a woman's temperature may be higher or lower when she is ovulating or having her menstrual period.

Below are average body temperatures based on age:

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 (37°C).

For children, fevers are a bit more complicated. Call your pediatrician if your child is:

Under 3 months and has a rectal temperature of 100.4 F or higher

Between 3 months and 3 years and has a rectal temperature over 102 F

Older than 3 years and has an oral temperature above 103 F

Between 3 and 6 months and -- along with a fever -- is fussier or more uncomfortable than usual, or doesn’t seem alert

Sick enough for you to be concerned, regardless of what the thermometer says

Fever facts:

Most fever is beneficial, causes no problems, and helps the body fight off infections. The main reason to treat a fever is to increase comfort.

Acetaminophen (Tylenol and others) and ibuprofen (Advil, Motrin) can be used to treat a fever. Aspirin should not be used in children or adolescents to control fever.

The prognosis for a fever depends on the cause. Most cases of fever are self-limited and resolve with the treatment of symptoms.

A person who is taking immunosuppressant drugs or who has a history of or diagnosis of cancer, AIDS, or other serious illness, such as heart disease or diabetes, should seek medical care if a fever develops.

What causes a fever?

Fever is the result of your immune system's response to a foreign invader. These foreign invaders include viruses, bacteria, fungi, drugs, or other toxins.

These foreign invaders are considered fever-producing substances (called pyrogens), which trigger the body's immune response. Pyrogens signal the hypothalamus in the brain to increase the body temperature set point in order to help the body fight off the infection.

What are the signs and symptoms of a fever?

A fever can cause a person to feel very uncomfortable. Signs and symptoms of a fever include the following:

Temperature greater than 100.4 F (38 C) in adults and children

Shivering, shaking, and chills

Aching muscles and joints or other body aches

Headache

Intermittent sweats or excessive sweating

Rapid heart rate and/or palpitations

How do health care professionals diagnose a fever?

Along with having generalized symptoms of fever, taking one's temperature with a thermometer can confirm the diagnosis of a fever. A temperature greater than 100.4 F in adults or children is considered a fever.

Different tests may be done by a doctor, such a blood and imaging tests, to determine the cause of fever, and if the cause of the fever needs to be treated.

What is the treatment for a fever?

Generally, if the fever does not cause discomfort, the fever itself need not be treated. It is not necessary to awaken an adult or child to treat a fever unless instructed to do so by a doctor.

The following over-the-counter fever-reducing medications may be used at home:

Naproxen (Aleve) is another nonsteroidal anti-inflammatory drug (NSAID) that can temporarily reduce fever. The adult dose is two tablets every 12 hours.

When should you worry about a fever?

A fever over 104 F/40 C in children and adults is considered dangerous. Seek medical attention immediately.

Any child below 3 months of age who has a temperature of 100.4 F (38 C) or greater should be seen by a physician. If a child or adult has a history or diagnosis of cancer, AIDS, or other serious illness, such as heart disease, diabetes, or is taking immunosuppressant drugs, medical care should be sought for a fever.

What kind of doctors treat a fever?

Any kind of doctor is able to treat a fever, but most likely when you have a fever you will see your family medicine specialist (also called a general practitioner) or internist, and your child will see a pediatrician. You may see an emergency medicine specialist in an emergency department.

What are the complications of a fever?

While having a fever is generally very uncomfortable, a fever itself does not usually cause severe complications.

High fever (>103 F/40 C) or prolonged bouts of fever can lead to:

seizures,

hallucinations, and/or

dehydration.

3 Possible ways to prevent a fever:

Prevention of fever is possible only to the extent that the specific cause of the fever can be prevented. Most fevers are caused by infection. Avoiding sources of infection and maintaining good hygiene practices are the best way to prevent a fever.

Some ways to prevent the spread of infection include the following:

Proper hygiene: Wash hands frequently.

Avoid contact with sick people.

Make sure immunizations are up to date.

What is the Normal Body Temperature for a Baby?

The American Academy of Pediatrics (AAP) states a normal body temperature for a healthy baby is between 97 and 100.3 degrees Fahrenheit. If the rectal temperature is 100.4 degrees or higher, they are considered to have a fever.

What is the Normal Body Temperature for Children?

The average normal body temperature for children is about 37°C (98.6°F). A child's temperature usually averages from around 36.3°C (97.4°F) in the morning to 37.6°C (99.6°F) in the afternoon.

What is the Normal Body Temperature for Adults?

The temperature in the mouth (oral) is about 36.8°C (98.2°F)

The temperature under the arm (axillary) is about 36.5°C (97.7°F)

The temperature in the anus (rectum/rectal), vagina, or in the ear (otic) is about 37.5°C (99.5°F)

What is Core Body Temperature?

Core temperature is the operating temperature of an organism, specifically in deep structures of the body such as the liver, in comparison to temperatures of peripheral tissues. Core temperature is normally maintained within a narrow range so that essential enzymatic reactions can occur.