A few moments in early parenthood feel quite as nerve-wracking as suspecting your baby might have a fever. Your little one feels warm against your cheek, and suddenly you're in the nursery, thermometer in hand, wondering if you're doing everything right. Knowing how to take a newborn's temperature accurately can bring real peace of mind.
A newborn's normal body temperature ranges between 97.9°F and 100.4°F (36.6°C to 38°C) when measured rectally. Any reading at or above 100.4°F (38°C) is considered a fever. For babies under 3 months old, even a low-grade fever warrants a call to your pediatrician right away.
What Is Normal Body Temperature for a Newborn?
A healthy newborn's temperature fluctuates throughout the day depending on activity, clothing, room temperature, and whether your baby was recently bathed or swaddled.
Why Temperature Varies in Newborns
Babies cannot regulate body heat the way older children can. Your newborn may run slightly warmer after crying, feeding, or spending time in breathable cotton sleepwear. Slight fluctuations within the normal range are common and usually not a cause for concern.
When a Reading Becomes a Fever
A rectal temperature of 100.4°F (38°C) or higher is classified as a fever in newborns by the American Academy of Pediatrics (AAP). For babies 3 months and younger, any fever at that threshold needs prompt medical attention, even if your baby seems well.
Which Thermometer Should You Use for a Newborn?
Not every thermometer type is accurate enough for a newborn, so choosing the right one matters.
A digital rectal thermometer is the most accurate option for infants under 3 months. Pediatricians recommend rectal readings because they reflect core body temperature. Look for a short, flexible probe designed for rectal use.
Temporal artery (forehead) thermometers can provide reasonably accurate results, but sunlight and sweat may affect the reading. Ear (tympanic) thermometers are not recommended for babies under 6 months because the ear canals are too small for an accurate seal. Armpit (axillary) readings serve as a quick first check, but tend to read lower and should be confirmed rectally if concern arises.
How to Take a Newborn's Temperature Rectally
A rectal reading is the gold standard for infants. The process is simpler than most parents expect.
Step-by-Step Instructions
- Wash the thermometer tip with soap and water, then rinse.
- Apply a small amount of petroleum jelly to the tip.
- Lay your baby on their back with knees bent toward the chest, or belly-down across your lap.
- Insert the tip about ½ inch to 1 inch into the rectum. Stop if you feel any resistance.
- Hold the thermometer steady between two fingers while cupping your baby's bottom.
- Wait for the beep, then note the temperature and time.
- Clean the thermometer and label it for rectal use only.
Speak softly while holding the thermometer in place. A familiar muslin swaddle blanket draped nearby provides comfort and warmth once you are finished.
When to Call Your Pediatrician About a Newborn's Fever
Approximately 2.6 million children under age 2 with fever present to U.S. emergency departments each year, according to the Western Journal of Emergency Medicine. Knowing when to seek help makes all the difference.
Fever Thresholds by Age
- Under 3 months: Call your pediatrician immediately for any rectal temperature of 100.4°F or higher.
- 3 to 6 months: Contact your doctor if the temperature reaches 101°F (38.3°C) or your baby seems unusually irritable.
- Over 6 months: Seek advice for temperatures above 102°F (38.9°C) or fevers lasting more than 24 hours.
Contact your pediatrician or visit the emergency room if your baby refuses to feed, has difficulty breathing, develops a rash, or shows signs of dehydration, such as fewer wet diapers.
How to Keep Your Baby Comfortable with a Fever
Dress your little one in light, breathable baby pajamas to help the body release heat naturally. Avoid overdressing. Offer breast milk or formula frequently in small amounts, and keep the room comfortable.
Never use rubbing alcohol baths or ice packs to bring down a fever. Alcohol can be absorbed through a baby's skin and cause serious harm. Always consult your pediatrician before giving any medication to an infant.
A gentle organic cotton receiving blanket provides warmth after temperature checks, and a burp cloth and bib combo keeps feeding time covered when your baby is under the weather. For dressing tips during any season, our guide on baby clothes for every season has you covered. Our article on new mom essentials for the first month is also a wonderful resource.
You've Got This, Mama
Every parent worries when their baby feels warm. Taking your newborn's temperature is one of those small skills that builds your confidence, one gentle reading at a time. Share this guide with a friend who is expecting, or save it for those middle-of-the-night moments. For more newborn care, our guide on how to swaddle your baby safely is a wonderful next read.
FAQs
1. What is the most accurate way to take a newborn's temperature?
A digital rectal thermometer provides the most accurate reading for infants under 3 months. Pediatricians recommend rectal readings because they reflect core body temperature.
2. Can I use a forehead thermometer on a newborn?
Yes, a forehead thermometer works as a first-pass check. Confirm the result with a rectal temperature if the reading is high or your baby seems unwell.
3. What temperature is a fever in a newborn?
A rectal temperature of 100.4°F (38°C) or higher is considered a fever. For babies under 3 months, any fever at that level requires an immediate call to your pediatrician.
4. How often should I check my newborn's temperature?
Only check when your baby feels warm, is fussy, or shows signs of illness. When monitoring a fever, check every 4 to 6 hours or as your pediatrician advises.
5. Should I take my baby's temperature after a bath?
Wait at least 20 to 30 minutes after a bath. A warm bath can temporarily raise skin temperature and give an inaccurate reading.
6. Is an armpit temperature reliable for a newborn?
An armpit reading works as a quick screen, but it is less accurate than rectal. If the reading shows 99°F (37.2°C) or higher, follow up with a rectal measurement.