You can take a temperature using the mouth (oral), anus (rectal), armpit (axillary), or ear (tympanic). But the temperature readings vary depending on which one you use, and you need an accurate body temperature to determine if a fever is present.
Medical research hasn't determined an exact correlation between oral, rectal, ear, armpit, and forehead temperature measurements. Generally, the correlation of temperature results are as follows:
The average normal oral temperature is 98.6°F (37°C).
A rectal temperature is 0.5°F (0.3°C) to 1°F (0.6°C) higher than an oral temperature.
An ear (tympanic) temperature is 0.5°F (0.3°C) to 1°F (0.6°C) higher than an oral temperature.
An armpit (axillary) temperature is usually 0.5°F (0.3°C) to 1°F (0.6°C) lower than an oral temperature.
A forehead (temporal) scanner is usually 0.5°F (0.3°C) to 1°F (0.6°C) lower than an oral temperature.
Rectal temperature is generally considered the most accurate temperature for examining young children.
The manufacturer of the temperature equipment you are using, such as an ear or Forehead Thermometer For a Adults, provides information on how to use it.Be sure to read and follow the instructions for an accurate temperature.This information can also include how the results of the device relate to the results of other temperature measurement methods.
Plastic strip thermometers have some USES, but they are not recommended for general household use. Unlike oral, rectal and ear thermometers, plastic strip thermometers measure skin temperature, not body temperature.If peripheral thermometers are used, about four out of every ten children have a fever.Clinicians should not rely on peripheral thermometers to influence clinical decisions.If there is no other option, consider that the actual temperature measured is at least +/ -1.5 °C and require repeated measurements.
When you discuss your temperature with your doctor, be sure to say which method is used to take your temperature. A rectal or ear temperature reading will be a little higher than an oral reading. A temperature taken in the armpit will be a little lower than an oral reading. The most accurate way to measure temperature is to take a rectal reading. Also, your normal temperature changes by as much as 1°F (0.6°C) 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.
The temperature comparison table below will give you the range of temperature correlation with the different methods used to take a temperature. For information about taking accurate temperatures in infants and children, see the topic Body Temperature.
To use the table:
Find the method that you used to take a temperature.
Find the correct temperature range.
Look for the temperature range of the other methods that correlates to the method you used. For example:
If your 2-year-old child's oral temperature is 101°F (38.3°C), his or her rectal or ear temperature may be about 102°F (38.9°C). Remember, a child has a fever when his or her temperature is 100.4°F (38°C) or higher, measured rectally.
If your axillary temperature is 100°F (37.8°C), your oral temperature is about 101°F (38.3°C).
Disclaimer: The views expressed in this commentary represent the views of the authors and not necessarily those of the host institution, the NHS, the NIHR, or the Department of Health and Social Care. The views are not a substitute for professional medical advice.