Adding one degree to temperatures taken under the arm when taking baby’s temperature

The situation with temperatures now being taken under the arm, in the ear, in the mouth, and in the rectum, checking for a fever has gotten a bit confusing. For instance, the rectum is normally warmer than under the arm—but how much warmer varies.

When talking to your doctor or nurse, tell them how you took the temperature and what reading you got. They can help you interpret the results. While 98.6 degrees F (37 degrees C) is considered the normal core body temperature, this value varies among individuals, among different areas of the body, and throughout the day. The daily variation is minimal in children less than six months of age, about 1 degree in children 6 months to two years old, and gradually increases to 2 degrees per day by age six.

A person’s baseline temperature is usually highest in the evening. Body temperature, especially in children, is normally raised by physical activity, eating, strong emotion, heavy clothing, elevated room temperature, and elevated humidity. A rectal temperature up to 100.4 degrees F (38 degrees C) may be entirely normal (no fever). However, lower values might be a fever, depending on the child.

If you get an under-arm reading over 99.5 degrees F (37.5 degrees C) and need to know if your child has a fever, it is best to retake the temperature using any of the other, more reliable methods.