The ability to monitor a baby’s body temperature offers parents and caregivers initial insight into their child’s health status. An elevated temperature often signals an infection, making accurate measurement necessary in pediatric care. While several body sites can be used, the axillary (underarm) method is widely favored for infants and young children because it is non-invasive and easy to perform. This technique provides a convenient screening tool to quickly determine if a child may have a fever.
Required Tools and Preparation
To ensure an accurate reading using the axillary method, a modern digital thermometer is required. These devices are safer and faster than older glass thermometers and are the standard for pediatric care. Before starting, clean the thermometer tip according to the manufacturer’s directions, typically with soap and warm water or rubbing alcohol, and then rinse.
Any clothing covering the armpit area must be removed so the thermometer touches the skin directly. The armpit must also be completely dry, as moisture can artificially lower the reading. If the baby was recently swaddled or submerged in warm water, wait 20 to 30 minutes to allow the skin temperature to normalize before taking the measurement.
Step-by-Step Guide to Axillary Measurement
The measurement process begins by holding the baby gently on your lap or laying them on their back on a firm surface. Turn the digital thermometer on, and place the probe tip directly into the center of the armpit fold. This ensures the bulb is fully enclosed by the skin.
Once positioned, hold the baby’s arm securely against their side and across the chest. This traps heat within the axillary space and keeps the thermometer stable.
The thermometer remains in place until it emits a beep or signal, which typically takes only a few seconds. After the signal, gently lift the arm and remove the thermometer to read the displayed temperature. Clean the thermometer immediately after use to maintain hygiene.
Interpreting the Temperature Reading
Axillary readings are generally lower than core body temperatures because this method measures external skin temperature, which does not perfectly reflect the body’s internal temperature. Medical professionals often suggest adding 0.5 to 1 degree Fahrenheit (or 0.3 to 0.6 degrees Celsius) to the axillary reading to estimate a more accurate internal temperature.
For infants, a normal axillary temperature typically ranges from 97.6°F to 99.6°F (36.4°C to 37.6°C). A reading of 99°F (37.2°C) or higher is generally considered a fever when measured under the arm. It is important to note the time the temperature was taken and report the exact reading, including the method used, to a healthcare provider.
A fever in a baby under three months is a particular concern. Any axillary reading of 99°F (37.2°C) or above in this age group warrants an immediate call to the pediatrician or a visit to an emergency facility. For babies between three and six months old, a temperature of 102°F (38.9°C) or higher, or a lower fever accompanied by lethargy, irritability, or other concerning symptoms, should also prompt a call to the doctor.
Limitations and Accuracy of the Armpit Method
The axillary method is considered the least accurate method for determining a baby’s true core body temperature. It functions best as a screening method to indicate the likely presence of a fever, rather than providing a definitive, precise measurement. This lack of precision means an elevated axillary reading often requires follow-up with a more accurate method, such as a rectal measurement, especially for very young infants or when serious illness is suspected.
External factors can compromise reliability. A cold room environment, a poor seal where the arm does not firmly close the armpit, or residual moisture on the skin can result in an artificially low reading. Conversely, being overdressed can cause the reading to be artificially high. If the baby appears visibly ill, regardless of a borderline or normal axillary temperature, medical consultation should not be delayed.