A rectal thermometer is a device which is inserted into the anus to measure body temperature. It is considered that a rectal thermometer provides most accurate body temperature. Generally it's used on children, especially infants (and babies) who can't hold a thermometer in their mouths. Also, a rectal thermometer can be used on adult patients who have suffered an oral injury or have undergone surgery in mouth or patients unable to take commands.

Most commonly used rectal thermometers are made of glass and contains mercury. Mercury further adds to accuracy element of these thermometers. Rectal temperature taking is most often performed by a person other than the patient. An accurate reading is vital for newborns and since the rectal method consistently gives the most accurate results, the doctors may ask you to take rectal readings until your baby turns 3 months old.

The first step you should take before using Rectal Thermometer is to thoroughly wash the thermometer in warm and soapy water. Rectal Mercury Thermometer should be shaken down so that the reading is well below 98 degrees F (36.67 degrees C). Insert thermometer only after applying lubricant like petroleum jelly or other water-based lubricants.

1. The most comfortable position for person having his temperature taken with a rectal thermometer is lying on the stomach. If one need to take temperature of a baby then he can lift the legs while the baby lies on his back.

2. Hold ready to use rectal thermometer in one hand and with your other hand, spread buttocks apart. Gently insert the bulb about three-quarters of an inch to an inch (2 to 2.5 centimeters) into the patient's rectum, or until the tip of the thermometer disappears (However, read the instruction that comes along with the product since the process of use may vary a little).

3. When using a mercury rectal thermometer, keep it in place for three minutes.

4. Remove the thermometer, hold at eye level and read it. The normal rectal temperature is 99.6 Fahrenheit (may vary slightly).