A person's body temperature is a vital sign that can indicate an underlying illness. However, the reliability of a temperature reading is influenced by the site and technique used. For clinical decisions, particularly in infants and young children, a precise measurement is crucial. Other methods offer convenience for a quick screening, though they may be less accurate.
Understanding Temperature Measurement: Core vs. Surface
Before diving into specific methods, it's important to differentiate between core and surface temperature. Core body temperature is the temperature of the internal organs and is considered the most accurate measure. Rectal and pulmonary artery thermometers measure core temperature directly. In contrast, other methods like oral or temporal (forehead) measure surface temperature, which can be affected by a variety of external factors.
The Gold Standard: Rectal Temperature
For infants (especially those under 3 months) and young children, the American Academy of Pediatrics recommends rectal temperature as the most accurate method. This is because it is the most reliable representation of core body heat. For adults needing a highly precise reading, it is also the best option.
How to take a rectal temperature:
- Use a dedicated digital thermometer with a short probe for rectal use only.
- Turn on the thermometer and lubricate the tip with petroleum jelly.
- Position the person face down on a flat surface or across your lap.
- Gently insert the thermometer tip about 1/2 to 1 inch into the rectum (1/2 inch for infants under 6 months).
- Hold the thermometer in place until it beeps.
- Hold the person still to prevent injury.
- Clean the thermometer thoroughly after use and label it to prevent oral use.
Note: Rectal temperatures are contraindicated for individuals with certain health conditions like leukemia or weakened immune systems.
Convenient and Reliable: Forehead (Temporal) Temperature
Temporal artery (forehead) thermometers are a popular option due to their speed and non-invasive nature. They use an infrared scanner to measure the temperature of the temporal artery on the forehead.
How to take a temporal temperature:
- Follow the specific instructions for your device, as some require a simple scan while others need the sensor to be held close to the skin.
- Place the sensor head at the center of the forehead and, for some models, slowly slide it toward the hairline near the top of the ear.
- Read the temperature on the display screen. Most provide a reading in seconds.
Forehead readings are generally considered the next most accurate after rectal, especially for infants over 3 months. However, their accuracy can be affected by external factors like a sweaty forehead, cold ambient temperatures, or direct sunlight.
Common and Easy: Oral Temperature
Oral temperature is a standard method for cooperative children over age 4 and adults. It is relatively accurate, but its reliability depends on correct placement and avoiding certain activities beforehand.
How to take an oral temperature:
- Wait at least 15-30 minutes after eating, drinking hot or cold fluids, or smoking.
- Place the tip of the digital thermometer under the tongue, towards the back of the mouth.
- Have the person close their lips around the thermometer and hold it with their lips, not their teeth, until it beeps.
Oral readings can be less accurate during a high fever when a person breathes through their mouth.
Fast for Older Children: Ear (Tympanic) Temperature
Tympanic (ear) thermometers measure infrared heat waves from the eardrum and provide a very quick reading. This method is suitable for children aged 6 months and older but is not recommended for infants due to narrow ear canals.
How to take an ear temperature:
- Pull the ear backward and up (for children over 1 year) to straighten the ear canal.
- Place the probe gently into the ear canal, aiming toward the eardrum.
- Wait for the device to beep.
Accuracy can be compromised by incorrect placement, earwax buildup, or recent outdoor cold exposure.
Least Accurate for Screening: Armpit (Axillary) Temperature
The armpit method is the least accurate and reliable option for measuring body temperature. It is generally used for screening purposes when other methods are not feasible.
How to take an armpit temperature:
- Place the tip of the digital thermometer in a dry armpit, ensuring it touches the skin, not clothing.
- Hold the arm close to the body for the recommended time until it beeps.
- Remember that this reading is typically lower than a core or oral temperature. If a fever is suspected, it is advisable to confirm with a more accurate method.
Comparison of Temperature Measurement Sites
| Method | Accuracy (Relative to Core) | Recommended Age | Pros | Cons |
|---|---|---|---|---|
| Rectal | Highest (Gold standard) | Infants (under 3 months), children up to age 4, adults needing high precision | Most accurate reading, reliable for infants | Invasive and uncomfortable, risk of injury if not done properly |
| Forehead (Temporal) | High (Second-most accurate) | All ages | Fast, non-invasive, hygienic, can be used on a sleeping child | Less accurate than rectal, can be affected by external factors |
| Oral | Medium-High (when done correctly) | Children over 4 years, adults | Widely accessible, easy to use for cooperative individuals | Inaccurate if taken too soon after eating/drinking, not for younger children |
| Ear (Tympanic) | Medium-High (when done correctly) | Children over 6 months, adults | Fast, less invasive than rectal | Placement must be precise, inaccurate for infants under 6 months, affected by earwax |
| Armpit (Axillary) | Lowest | All ages (screening only) | Non-invasive, safe | Least accurate, should be confirmed with another method if fever is suspected |
Which method should you choose?
- For infants under 3 months: Rectal is the most accurate and recommended method for clinical decisions, especially if a fever is suspected.
- For children 3 months to 4 years: Rectal or forehead measurements are accurate. Ear thermometers can also be used after 6 months.
- For children over 4 years and adults: Oral is a reliable option, but forehead or ear can also be used, depending on personal preference.
- For screening purposes or non-cooperative individuals: The forehead or armpit methods offer a quick, low-stress option, but be aware of their limitations.
Consistency is Key
Regardless of the method you choose, it's most important to be consistent. Always use the same method and site when tracking a temperature trend to ensure reliable comparison of readings. If you switch between methods, be aware of the typical variations between sites (e.g., rectal is higher than oral). When reporting a temperature to a healthcare provider, always state the method and site used.
For more detailed information on measuring temperature, consult the resources available from reputable organizations like MedlinePlus.
Conclusion
The most accurate site to take a temperature is rectally, particularly for infants under 3 months, as it provides the truest measure of core body temperature. However, modern digital forehead and ear thermometers are also reliable and convenient options for older children and adults when used correctly. Oral measurements offer another accessible option for those over age 4. Armpit readings are the least accurate and should only be used for a quick initial screening. Choosing the right method depends on the person's age, comfort level, and the necessary level of accuracy, but consistency in your approach is always crucial for accurate monitoring.
