How to take your temperature in 5 different ways — and which is most accurate to detect a fever

• To take temperature safely, you should use a digital thermometer.
• To get an accurate temperature for children under three years old, you should use a rectal thermometer for best results.
• For everyone else, oral thermometers are the best option for accurate temperature results.

Although you probably only take your temperature when you're not feeling well, it may also be helpful to take it on a regular basis. This will make you aware of your normal body temperature and better able to determine when you have a fever, which is usually a warning sign of an infection or illness.

Your body temperature changes throughout the day. It's usually lower in the morning and highest in the late afternoon and evening. For consistency, you should take your temperature at the same time every day. Wait for 30 minutes to take your temperature after eating, drinking, or exercising.

When taking your temperature, it's important to always use a digital thermometer instead of a glass one because of the potential for exposure to toxic mercury if the glass breaks. Because of this danger, the sale of mercury thermometers has even been banned in some states.

Still, there are many different ways to take your temperature with a digital thermometer. Here's how to do it:

Oral

Oral digital thermometers use electronic heat sensors to measure your body temperature. Taking your temperature orally is the most effective method for adults, according to internal medicine specialist Michelle N. Brooks, MD, an assistant professor and academic hospitalist at VCU Health.

Oral thermometers can also be used for children over the age of 4 who are able to keep their mouth closed while their temperature is being taken, so that the reading is accurate.

To take your temperature orally, do the following:

1. Turn on the thermometer and place the tip under your tongue toward the back of your mouth.
2. Close your lips around the thermometer.
3. Hold the thermometer in place using your lips and fingers. Don't bite it.
4. After one minute, or when the thermometer beeps, remove it from your mouth and read the temperature.

Ear

Ear thermometers, also known as tympanic thermometers, measure the infrared heat waves from the eardrum. They can be used for infants older than 6 months, children, and adults. They aren't recommended for younger infants because their ear canals are too small for an accurate reading.

If you or your child has an earache, you should use the ear thermometer in the other ear to prevent further pain and because inflammation from an ear infection may result in a slightly higher temperature reading.

Follow these steps to take your ear temperature:

1. Make sure the ear canal is free of earwax, which can interfere with the temperature reading.
2. Gently pull the ear up and back to help straighten the ear canal.
3. Turn on the thermometer and insert the probe until the ear canal is sealed off, or no further than the instructions indicate.
4. Hold it in place until it beeps.
5. Remove it and read the temperature.

Forehead

These thermometers, also called temporal artery thermometers, measure infrared heat waves coming from the blood vessel located under the skin across your forehead. They can be used for infants older than 3 months, children, and adults.

However, the temperature reading can be affected by direct sunlight or cold outdoor temperatures. A small 2014 study of 100 adult patients in an emergency department also found that for 47 patients who had fevers, 57% of the fevers were recorded by an oral thermometer but not by a forehead thermometer.

To use a forehead thermometer, do the following:

1. Turn on the thermometer.
2. Depending on the thermometer's instructions, either aim the sensor at one spot on the forehead, or gently sweep it from the center of the forehead to the top of an ear.
3. Read the temperature on the thermometer.

Rectal

"For newborns and infants, we typically take rectal temperatures," says Monique May, MD, a family physician based in Charlotte, NC. Rectal thermometers are recommended for children under 3 years old by the American Academy of Pediatrics because they take the most accurate readings.

Be sure to use a different digital thermometer for taking temperatures orally.

To use a rectal thermometer on your baby, do the following:

1. Put a dab of petroleum jelly or another lubricant on the tip of the thermometer.
2. Place your infant on their back, using your hand to bend their legs toward their chest, or place your infant belly-side down across your lap, keeping your hand on their lower back.
3. Gently insert the thermometer up to an inch into your infant's rectum. Stop if you feel resistance.
4. Leave the thermometer in place until it beeps. Remove it and read the temperature.

Armpit

This temperature is less accurate than an oral or rectal temperature. It can be taken for children and adults by using a digital thermometer.

To take an armpit temperature, do the following:

1. Turn on the thermometer and place the tip in your armpit, making sure it's not touching any clothing.
2. Hold it tightly in place. For children, hug your child and keep their side that's holding the thermometer against your chest.
3. When the thermometer beeps, remove it and read the temperature.

How to clean a thermometer

It's important to always clean your thermometer after using it to prevent spreading germs, especially if you may be sick.

Be sure to first check the manufacturer's instructions, but most digital thermometers can be disinfected by either using rubbing alcohol that's at least 60% alcohol to kill bacteria, or a bleach or alcohol wipe.

To clean an oral or rectal digital thermometer, do the following:

1. Using a cotton ball or pad soaked in rubbing alcohol, or an alcohol or bleach wipe, rub the entire length of the thermometer, avoiding the digital display.
2. Let the thermometer air dry or wipe it with a clean cloth.

To clean an ear or forehead thermometer, do the following:

1. Using a cotton ball or pad soaked in rubbing alcohol, or an alcohol or bleach wipe, wipe down the thermometer's probe or sensor.
2. Let the thermometer air dry or wipe the probe or sensor with a clean cloth.

When to see a doctor

If your baby is less than 3 months old and has a temperature of 100.4°F or higher, get medical help immediately. For children or adults, you should see a doctor if your temperature is above 104°F. You should also see a doctor if your child shows any symptoms of dehydration, such as having a dry diaper for over eight hours or crying without tears.

You should also see a doctor if you or a child has any of the following symptoms along with the fever, which could indicate a serious health problem like pneumonia or meningitis:

• Difficulty breathing
• Chest pain
• Severe headache
• Confusion
• Repeated vomiting
• A stiff neck or sensitivity to light
• Skin rash

A fever will usually go away on its own after one to three days. If it persists for more than a week, May says you should see a doctor. Your child should see a doctor if their fever lasts for more than five days.

Insider's takeaway

It's important to know how to take your temperature in order to check for a fever. For children under three years old, it's most accurate to use a rectal thermometer. Everyone else should use an oral thermometer for the most accurate results.

Related articles from Health Reference:

• How to tell if you have a fever without a thermometer
• What causes a fever and when to seek medical attention
• How to break a fever and help alleviate your symptoms
• What is normal body temperature? How to know if you have a fever
• You're probably not washing your hands long enough, and it could be making you sick