Thermometer measuring hypothermia. Clinical thermometer calibrated in degrees Fahrenheit (F) and Celsius (C), showing hypothermia. The temperature seen is below 95 F (35 C). A fall in body temperature to below 35 C is known as hypothermia, measured in the mouth, underarm or rectum. Hypothermia is caused by insufficient heating of the body. It leads to drowsiness, a lower breathing and heart rate, and may result in unconsciousness and even death. The thermometer consists of a sealed narrow-bore glass tube with a bulb at one end. Mercury inside the tube expands when heated and extends along the scale. This thermometer measures temperatures of 94-108 F.