Vital Signs

Body Temperature

Also written as: Temp

The body's core heat level, which normally varies by time of day and measurement site.

What it measures

How warm the body's core is, estimated from the mouth, ear, forehead, armpit, or rectum. Each site reads a little differently, and the body normally moves its temperature up and down through the day.

Why it is checked

Checked to detect fever, which is a deliberate immune response and a common early sign of infection or inflammation, and to track the course of an illness. It is also used to spot abnormally low temperature, which matters in cold exposure and in serious illness.

What is generally associated with a higher result

Broadly associated with infection and inflammation, since fever is part of the immune response, and also with recent vigorous exercise, hot environments, heavy clothing, and certain phases of the menstrual cycle. Some medications are also broadly associated with raised temperature.

What is generally associated with a lower result

Broadly associated with cold exposure, an underactive thyroid, and some medications. Slightly lower readings are also common in older adults and vary with the site being measured.

Everyday things that move this number

Not every shift in a value reflects disease. These are ordinary factors known to affect this particular measurement:

• Time of day, since temperature normally runs lower in the early morning and higher in the evening
• Hot or cold drinks shortly before an oral reading
• The site measured (mouth, ear, forehead, armpit, rectum) and the type of thermometer
• Exercise, a hot bath, or warm clothing beforehand
• Menstrual cycle phase and pregnancy

Questions to take to your appointment

• Which thermometer type and body site gives the most dependable reading at home?
• For someone my age and health, when does a raised temperature warrant a call or visit?
• Could any of my regular medicines mask a fever or cause one?

Build a printable questionnaire with your own results →

Where to read more

MedlinePlus, from the US National Library of Medicine, publishes patient-facing pages on individual lab tests and is a reliable next stop: medlineplus.gov/lab-tests .

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