A fever can be a sign of an infection or other medical condition, so it is useful to check body temperature with a thermometer. Temperatures can be checked in the mouth, rectum, armpit, and ear as well as across the forehead. Thermometers use a variety of technologies to measure body temperature. The oldest technology is the mercury-in-glass thermometer. Newer technologies include non-mercury liquids-in-glass as well as digital and electronic devices that use sensors to measure temperature. Thermometers that check body temperature in the ear, across the forehead, or have a digital display do not contain mercury. The EPA recommends the use of mercury-free thermometers but it does not endorse any specific brand and suggests choosing a thermometer that is easy to use and read. A recent study found that the most accurate way to measure body temperature is with a rectal thermometer. However, the authors of the study say that when the rectal route is impractical or should be avoided, electronic thermometers that are placed in the mouth or in the ear are reasonable alternatives.
Potentially harmful effects from broken thermometers vary depending on the type of thermometer. The most concerning are mercury-containing thermometers. The least concerning are the digital/electronic thermometers because they contain no potentially hazardous liquids that can spill if broken. However, many of the electronic thermometers contain button cell batteries which can be very harmful if swallowed. If a battery is swallowed, contact the battery ingestion hotline at 800-498-8666.
Common to all the liquid-in-glass thermometers is the potential for injury from the broken glass. Studies of children in emergency rooms have noted injury to the mouth, rectum, and ear from broken thermometer glass. Otherwise the potential toxicity from these broken thermometers depends on the type of liquid used.
If you have a liquid-in-glass thermometer, it is important to be able to tell if it contains mercury. A few simple steps can help. If the liquid is not silver in color, it does not contain mercury. If the liquid is silver in color it might be mercury. Spilled mercury has a characteristic appearance. It is a dense, shiny, fast-moving liquid metal that can break up into little balls that reform when pushed together. But not all thermometers with silver liquid contain mercury. There are liquid-in-glass thermometers that contain a non-mercury silver substance (Galinstan®) that, according to its maker, is not toxic when swallowed because it passes through the digestive system without effect. Inhalation is also not a concern because there is no absorption through the lungs. If the thermometer has silver liquid and is not labeled as “mercury-free,” assume it contains mercury.