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Monitoring your body temperature can tell you important things about your health.

Normal body temperature runs around 98.6°F (37°C), on average. However, some people have a body temperature that’s a bit warmer or cooler, and that’s normal.

Having a temperature that’s much warmer or cooler, though, may indicate some kind of health problem, such as fever caused by infection, or low body temperature caused by hypothermia.

Body temperature is often measured by placing a thermometer in the mouth. But there are four other ways to take body temperature, and these involve different body parts:

  • ear (tympanic)
  • forehead
  • anus (rectal)
  • under the armpit (axillary)

Ear, oral, and rectal temperatures are considered the most accurate readings of actual body temperature.

Underarm (axillary) and forehead temperatures are considered to be the least accurate because they’re taken outside of the body rather than inside. These temperatures can be as much as a full degree lower than oral body temperature.

But just because underarm temperature isn’t very precise doesn’t mean that it isn’t useful. It can be a good way to screen for changes in body temperature.

A digital thermometer is useful for taking underarm temperature. Don’t use a mercury thermometer, which can be dangerous if it breaks.

To measure underarm temperature:

  1. Check that the thermometer is on.
  2. Lightly press the tip of the thermometer into the center of the armpit.
  3. Hold your arm, or your child’s arm, close against the body so the thermometer stays in place.
  4. Wait for the thermometer to take its reading. This will take about a minute, or until it beeps.
  5. Remove the thermometer from the armpit and read the temperature.
  6. Clean the thermometer and store for its next use.

When taking axillary temperature, it can be useful to compare it to ear, oral, and rectal temperature readings, which are more precise.

Use the following chart to find the ear, oral, or rectal reading that corresponds to the axillary reading.

Axillary temperatureOral temperatureRectal & ear temperature
98.4–99.3°F (36.9–37.4°C)99.5–99.9°F (37.5–37.7°C)100.4–101°F (38–38.3°C)
99.4–101.1°F (37.4–38.4°C)100–101.5°F (37.8–38.6°C)101.1–102.4°F (38.4–39.1°C)
101.2–102°F (38.4–38.9°C)101.6–102.4°F (38.7–39.1°C)102.5–103.5°F (39.2–39.7°C)
102.1–103.1°F (38.9–39.5°C)102.5–103.5°F (39.2–39.7°C)103.6–104.6°F (39.8–40.3°C)
103.2–104°F (39.6–40°C)103.6–104.6°F (39.8–40.3°C)104.7–105.6°F (40.4–40.9°C)

Underarm temperature is considered the safest way to check the body temperature of children under 3 months old. It’s also commonly used to check temperature in infants to 5-year-olds because it’s one of the easiest, least invasive methods.

Take a child’s underarm temperature the same way you’d take your own. Hold the thermometer to keep it in place, and make sure they don’t move around while the thermometer is underneath their arm, which can throw off the reading.

If their temperature reads higher than 99°F (37°C), confirm this temperature using a rectal thermometer, as your child may have a fever.

Taking rectal temperature is a safe way to get a very accurate body temperature reading in young children. It’s important to confirm fever as quickly as possible in young children, and to get them to a doctor as soon as possible once one is detected.

To take a child’s rectal temperature:

  1. Clean the digital thermometer with cool water and soap, and rinse thoroughly.
  2. Cover the end (silver tip) with petroleum jelly.
  3. Put your child on their back with knees bent.
  4. Carefully insert the end of the thermometer into the rectum to about 1 inch, or 1/2 inch if they’re less than 6 months old. Hold the thermometer in place with your fingers.
  5. Wait about 1 minute or until the thermometer beeps.
  6. Slowly remove the thermometer and read the temperature.
  7. Clean the thermometer and store for next use.

Ear thermometers are also safe to use in children over 6 months. Oral thermometers aren’t recommended for young children, as they often have trouble keeping the thermometer under their tongue long enough for a temperature reading to be taken.

It’s considered safe to take a child’s forehead temperature, but be sure to use a forehead thermometer made for this purpose and not forehead strips.

Age can affect normal body temperature. The following chart shows normal body temperature when taken in the underarm.

Age range (years)Normal temperature range for underarm temperatureTemperature considered fever
0–294.5–99°F (34.7–37.2°C)99.1°F+ (37.3°C+)
3–1096.6–98.0°F (35.9–36.7°C)98.1°F+ (36.7°C+)
11–6595.3–98.4°F (35.2–36.9°C)98.5°F+ (36.9°C+)
65+96.0–97.4°F (35.6–36.3°C)97.5°F+ (36.4°C+)

There are several ways to measure a person’s body temperature. Here’s how to measure temperature in areas other than the underarm:

Ear

Ear temperature usually reads a bit lower than rectal temperature. To take ear temperature, you need a special ear thermometer. Here’s how to use it:

  1. Add a clean probe tip to the thermometer and turn it on using the manufacturer’s instructions.
  2. Tug softly on the outer ear so that it’s pulled back, and gently push the thermometer into the ear canal until it’s fully inserted
  3. Press the thermometer’s temperature reading button down for 1 second.
  4. Remove the thermometer carefully and read the temperature.

Forehead

Forehead temperature is the next most accurate reading behind ear, oral, and rectal temperatures. It also doesn’t cause much discomfort, and getting a reading is very fast.

To take forehead temperature, use a forehead thermometer. Most slide across the forehead. To use it:

  1. Turn on the thermometer, and place the sensor head at the center of the forehead.
  2. Slide the thermometer slowly across the forehead toward the top of one ear, keeping it in contact with the skin at all times.
  3. Stop moving the thermometer once you reach the hairline.
  4. Read the temperature on the display reading.

Forehead strips aren’t considered an accurate way of reading forehead temperature. You should use a forehead thermometer instead.

Shop for ear and forehead thermometers online.

Mouth

Oral temperature is considered to be almost as accurate as rectal temperature, and it’s the most common way to measure temperature in older children and adults.

To take oral temperature, use a digital thermometer. Wait at least 30 minutes to use an oral thermometer if you’ve eaten or had something hot or cold.

  1. Place the thermometer under one side of the tongue toward the back of the mouth, making sure the tip is completely under the tongue at all times.
  2. Hold the thermometer in place with the lips and fingers. Avoid using the teeth to keep the thermometer in place. Seal the lips for up to a minute or until the thermometer beeps.
  3. Read the thermometer and clean it before putting away.

Rectum

Rectal temperature is considered the most accurate temperature reading. This is most useful for keeping track of temperature in children, who tend to be more sensitive to changes in body temperature than adults.

The steps for taking a child’s rectal temperature are outlined above in the section “How to measure an infant or toddler’s temperature.”

Never use the same rectal thermometer to take an oral temperature. Make sure the thermometers are clearly marked, which can prevent you or someone else from accidentally using it in your child’s mouth.

Shop for digital thermometers, which can be used to take oral, rectal, or underarm temperatures, online.

Normal body temperature may be a bit warmer or cooler than the average, 98.6°F (37°C), and how you measure that temperature also affects what’s normal.

However, the general guidelines show what’s considered a fever using the different body temperature measurement methods:

Measuring methodFever
Ear100.4°F+ (38°C+)
Forehead100.4°F+ (38°C+)
Mouth100°F+ (38.8°C+)
Rectum100.4°F+ (38°C+)
Underarm99°F+ (37.2°C+)

Symptoms of a fever depend on its cause. Some causes include viruses, bacterial infections, and other disease. Yet, some of the most common symptoms with various causes include:

  • chills
  • dehydration
  • headache
  • irritability
  • loss of appetite
  • muscle aches
  • shivering
  • sweating
  • weakness

Children between 6 months and 5 years of age might also experience febrile (fever) seizures. According to the Mayo Clinic, about a third of children who have one febrile seizure will experience another, often within the following 12 months.

Fevers can be dangerous, especially in babies, young children, and older adults. Seek prompt medical advice if your child shows any signs of fever, especially an elevated body temperature.

There are some things you can do at home to bring down your child’s body temperature when waiting for medical help.

Older adults should also seek prompt medical help for a fever. Otherwise healthy adults should also seek help for a high fever, or a fever that lasts longer than a day.

One of the most common causes of fever is infection, which requires immediate medical attention to treat. A course of antibiotics can usually wipe out the infection that’s causing a fever.

Fever can cause life-threatening seizures, especially in infants and children. Seek medical guidance if your child has a fever.

Low body temperature can also be a cause for concern.

Medical emergency

If you or your child has a very low body temperature, they could be experiencing issues with their body circulation or cold exposure. Both of these issues require immediate medical attention.

There are several ways to take a person’s body temperature, each with varying degrees of accuracy. Using underarm temperature is a safe and effective way to monitor body temperature, especially in younger children.

However, it isn’t the most accurate method. So if you suspect a fever in a young child, it’s best to reconfirm their body temperature using a rectal thermometer. Prompt treatment of fever and its causes can reduce the risks of fever symptoms and possible complications.