A rectal thermometer is one means of taking body temperature. It is usually thought to give an extremely accurate reading, but since it is inserted into the anus, not all people prefer this method of taking temperatures. Squeamish parents can take an axillary temperature in the armpit or use ear or forehead temperatures if they prefer to avoid taking a child's temperature rectally. Up until recently, most rectal thermometers were made of glass and contained mercury. These are now considered unsafe for use, and old ones should be disposed of properly.
Fever may be an indicator of illness. The three best ways to measure body temperature are rectally, orally, or with a tympanic thermometer ear. In infants under 3 months old, only take a rectal temperature.
The measurement of body temperature can help detect illness. It can also monitor whether or not treatment is working. A high temperature is a fever.