Pick a glass thermometer without mercury. If you have the option, a non-mercury glass thermometer is safer. It should say on the package whether it contains mercury or not, so read it carefully.[2] X Research source A non-mercury thermometer is safer because it can't leak mercury. However, as long as you inspect the thermometer to ensure there are no cracks or leaks, a mercury thermometer should also be safe. Choose between a rectal or oral thermometer. These thermometers have different tips to make it more comfortable for the person or child who's temperature you're taking. Look for a rounded tip on a rectal thermometer or a longer, narrow tip for an oral thermometer.[3] X Research source They're often color-coded on the other end, red for anal and green for oral. You can also read the packaging to find out what kind you have. Clean the thermometer with soap and water. Use cool water and any kind of hand soap or dish soap and rub it up and down on the thermometer to clean it. Rinse it thoroughly under running water to get rid of any soap residue.[4] X Trustworthy Source PubMed Central Journal archive from the U.S. National Institutes of Health Go to source Don't use hot water, as

you could rupture the thermometer. You can also cleanse the thermometer by wiping it down thoroughly with rubbing alcohol and then rinsing it off. Shake the thermometer to lower the temperature. Glass thermometers don't always reset themselves after you take a temperature. Grab it at the end away from the tip and swing the thermometer back and forth. Check to make sure it goes down below at least 96.8 °F (36.0 °C); it needs to be under the average body temperature.[5] X Trustworthy Source PubMed Central Journal archive from the U.S. National Institutes of Health Go to source Take a rectal temperature if the person is under 5 years of age. Lubricate the tip with a bit of petroleum jelly. Place the child on their back with their legs up. Gently push the tip into the rectum, going about 0.5 to 1 inch (1.3 to 2.5 cm) in. Never force it in if it feels blocked. Hold it in place the whole time you're taking the reading, as you don't want to go deeper into their body.[6] X Trustworthy Source Mayo Clinic Educational website from one of the world's leading hospitals Go to source Hold the baby or child still so that the thermometer doesn't break.[7] X Trustworthy Source Mayo Clinic

Educational website from one of the world's leading hospitals Go to source Children may bite down on a thermometer if it's in their mouths, leading to glass shards and mercury in their mouths, which is why you shouldn't place a glass thermometer in their mouth. Plus, a rectal temperature is the most accurate for children.[8] X Trustworthy Source PubMed Central Journal archive from the U.S. National Institutes of Health Go to source Place the thermometer under the armpit for a simpler way to take a child's temperature. For this type, use an oral or a rectal thermometer. Lift the person's arm and set the thermometer so that the tip is directly in the center of the armpit. Have the person hold their arm tightly against their body.[9] X Trustworthy Source PubMed Central Journal archive from the U.S. National Institutes of Health Go to source If the temperature indicates the person has a fever, you should check it again with a rectal or oral reading, depending on the age of the person, as those are more accurate. Use an oral thermometer for kids over 5 and adults. Put the tip of the thermometer under the person's tongue. Have them hold it in place while the thermometer warms up to their

body temperature.[10] X Trustworthy Source PubMed Central Journal archive from the U.S. National Institutes of Health Go to source This method is accurate, but it can be difficult for some kids to hold it in place properly. Leave the thermometer in place for the appropriate amount of time. The amount of time depends on the location. If you're using a rectal thermometer, 2-3 minutes is enough time. In the mouth or under the armpit, leave the thermometer in place for 3-4 minutes.[11] X Trustworthy Source PubMed Central Journal archive from the U.S. National Institutes of Health Go to source Try not to shake the thermometer as you pull it out, as this could affect the reading. Hold the thermometer horizontally so you can read the numbers. Bring it up to eye level with the end of the liquid right in front of you. Look for the long lines, which indicate 1 °F (?17 °C) each and the smaller lines, which indicate 0.2 °F (?17.7 °C) each. Read the nearest number to the end of the liquid, counting the small lines if you need to.[12] X Research source For instance, if the end of the liquid goes past the larger 100 °F (38 °C) mark by 2 smaller lines, then the temperature is 100.4 °F (38.0

°C). Determine if the person has a fever. Typically, you or your child has a temperature if it's 100.4 °F (38.0 °C) when taken in the rectum, 100 °F (38 °C) when taken in the mouth, or 99 °F (37 °C) when taken under the armpit. These are the minimum temperatures for a fever.[13] X Trustworthy Source Mayo Clinic Educational website from one of the world's leading hospitals Go to source Call the doctor if your child is under 3 months and running a fever based on a rectal reading. If your child is 3-6 months and is running a temperature of 102 °F (39 °C), talk to your doctor, particularly if your child is showing other symptoms like lethargy or crankiness. If it goes above 102 °F (39 °C), contact your doctor no matter what. If your child has a temperature of 102 °F (39 °C) and is 6 to 24 months, call your doctor if it lasts more than a day. Also, call if your child is showing other signs of sickness, such as coughing or diarrhea. If you have an older child or an adult, go to the doctor for a temperature of 103 °F (39 °C) or higher. Clean the thermometer again before putting it away. Wash it with cool water and soap, rubbing the length of the thermometer but focusing

especially on the tip. Rinse it thoroughly with water when you're done.[14] X Research source If you don't clean it, you could introduce germs to the next person who uses it.