Checking an infant’s temperature

Ever notice when a baby’s cheeks start feeling a little warmer than usual? Maybe they’re just cozy — or maybe they’re starting to come down with something. In these moments, having information about checking an infant’s temperature can offer some much-needed peace of mind to caregivers.

In this article:

Types of baby thermometers

There are several types of thermometers that may be used when checking a child's temperature, but which type to use may depend on several factors.

• Digital thermometers (oral, rectum or armpit). These devices use sensors to read body temperature. They're versatile, too; some products are made as multi-use thermometers. For those products, caregivers can use them in the mouth, rectum or under the arm for a gentler approach. But make sure to label the thermometer so it is not used in both the mouth and rectum without being cleaned as directed by the package label. Under-the-arm (axillary) thermometers may be a gentle way to start. They're noninvasive and can be easy to use, even if they're not the most precise. Rectal thermometers give the most accurate readings, especially for children under 3 months. Oral thermometers are not recommended until a child is age 4 or older.
• Temporal artery thermometers (forehead). Forehead thermometers are another option to use for newborns and children of any age. These devices use infrared technology to measure heat from the baby’s forehead. They scan the temporal artery, which runs just beneath the skin, making it a speedy and noninvasive choice (especially handy during naptime)!
• Tympanic (ear) thermometers. Starting when babies are 6 months old, digital ear thermometers, which use infrared technology to measure heat waves from the eardrum, can be used. When the thermometer is placed correctly in the ear, readings can be accurate.

Ways to take a baby’s temperature

Below are some common ways to take a baby’s temperature, along with explanations of the different ways to use each thermometer safely. It is recommended that caregivers follow the manufacturer instructions on the thermometer’s packaging.

Rectal temperature

Taking a baby's temperature rectally involves gently placing a digital thermometer into the rectum to capture a temperature reading. A small amount of petroleum (a lubricant) is typically added to the tip, although it is best to follow manufacturer instructions for use. The device stays in place until it beeps or signals that the temperature reading is complete. 

Underarm temperature 

Taking a temperature in the armpit — called an axillary temperature — can be a quick and noninvasive way to check for a fever in babies. While it’s not the most accurate method, it may be a helpful first step, especially in public settings like day care.

Ear temperature 

Ear thermometers can be a convenient and accurate way to check for fever. But they should not be used before a baby is a least 6 months old because their ear canals are too narrow.

Tip: Finding the right spot in tiny ears can take practice. It’s okay to double-check for a fever with a rectal thermometer or reach out to a health care provider.

Forehead (temporal artery) temperature

Forehead (temporal artery) thermometers are a noninvasive way to check a baby’s temperature. They can work well for children of all ages and can be used as a first pass for younger infants who show signs of illness.

Tips on taking a baby’s temperature

Before using a thermometer, a few simple steps can help ensure the temperature reading is accurate:

• If a baby just took a bath, has been swaddled, has been under blankets or was dressed in layers, it's best to wait 20 to 30 minutes before taking their temperature.
• If a baby just came inside the house from a hot or cold day, sweat and cold air might affect how accurate the reading is.
• For oral temperatures, wait 30 minutes if the child has just had a hot or cold drink.
• Caregivers should opt for a digital thermometer — they’re safer than glass ones. Mercury thermometers are no longer recommended, as mercury is a toxic metal. If the glass breaks, the toxin might escape. Most modern digital thermometers work fast and are easy to use.
• Tips of thermometers should be washed with soap and water, then rinsed and dried before and after use, especially with rectal thermometers. It is important to follow the directions for cleaning and disinfecting that are on the package label. Cleaning helps remove germs and bacteria that may be on the thermometer and might help prevent infections. To avoid cross use, caregivers with multiple thermometers can also label them. For example, one for rectal use and another for oral use.
• Making sure infants aren’t in direct sunlight or cold temperatures can help take a more accurate forehead temperature reading. 

When to visit a health care provider

A caregiver might visit a health care provider when their baby has a high fever. A fever can be a sign that the body is working hard to fight off an illness. While a fever might feel worrisome, it’s not always a bad thing. Still, knowing when to check in with a health care provider is important, especially for the tiniest ones.

If a baby seems unwell, or if they are 2 months old or younger and the reading suggests a temperature of over 100.4 degrees Fahrenheit, it's a good idea to follow up with a health care provider right away. Caregivers should also see a health care provider for children of any age if they have a fever above 104 degrees Fahrenheit.

Here’s what counts as a fever, depending on how it’s measured:

There are special instances when a caregiver should check in with a health care provider quickly, such as when a baby is 3 months or younger and has a rectal temperature of 100.4 degrees Fahrenheit (equivalent to 38 degrees Celsius) or higher.

If a child is older than 6 months and they're drinking fluids, sleeping well and still playful, there may not be a need to treat the fever right away (unless the child is uncomfortable). Instead, caregivers could wait to see if their fever gets better with time.

Caregivers can check with a health care provider about next steps, including treatment. Some fever-reducing medications may be recommended for children 6 months and older. If using an over-the-counter (OTC) option, they should follow the label instructions carefully for the right dose.

Key takeaways

Caring for a baby means tuning in to the small signals — like warm cheeks or a change in mood — and knowing when to take the next step. By understanding how to check a temperature accurately and having the right thermometer for the job, caregivers can respond with confidence and calm. And even uncertain moments can become opportunities to support a little one’s health and well-being.