Newborn Fever: When a Temperature Is an Emergency
Share
A rectal temperature of 100.4°F (38°C) or higher in a baby 3 months old or younger requires prompt medical evaluation. Call your pediatrician or other medical professional immediately for instructions. Do not wait for the temperature to rise higher, and do not wait to see whether your baby develops additional symptoms.
- In a baby 3 months old or younger, a confirmed fever requires prompt medical evaluation.
- A rectal temperature of 100.4°F (38°C) or higher is considered a fever.
- Do not rely on touch alone to decide whether your newborn has a fever.
- For young infants, a rectal temperature provides the most reliable measurement.
- Do not wait for the temperature to become higher before calling.
- Do not give fever medicine before calling unless your pediatrician has specifically instructed you to do so.
- A young baby can look surprisingly well and still have a potentially serious infection.
Fever is handled differently in a newborn than it is in an older baby or child.
With an older child, parents can often watch how the child is behaving, encourage fluids, and monitor symptoms for a period of time.
A young infant is different. Because serious bacterial infections can initially produce very few symptoms, a fever in the first months of life deserves prompt medical attention.
The temperature itself is important, but so are your baby's age, feeding, alertness, breathing, hydration, and overall appearance.
What Temperature Is Considered a Fever in a Newborn?
A temperature of 100.4°F (38°C) or higher is considered a fever in a young infant.
For babies 3 months old or younger, that threshold is important because fever can occasionally be the first sign of a serious infection.
You do not need to wait for the temperature to reach 101°F, 102°F, or higher. Once a reliable rectal temperature reaches 100.4°F (38°C), contact your pediatrician or other medical professional promptly.
Why Is Fever More Concerning in a Young Infant?
Young infants have immature immune systems and may not show the same obvious signs of illness that older children do.
A significant infection may initially cause little more than fever.
Doctors therefore use a lower threshold for evaluating fever in very young babies because infections involving the bloodstream, urinary tract, lungs, or central nervous system can occasionally occur.
Most young infants with fever will not have one of these serious infections. The reason prompt evaluation is recommended is to identify the smaller group who may need testing or treatment.
What Is the Best Way to Take a Newborn's Temperature?
For infants younger than 3 months, a digital rectal thermometer provides the most reliable temperature measurement.
Forehead and underarm measurements can sometimes be useful for screening, but they may not be as dependable when an exact temperature matters.
Ear thermometers are generally not recommended for newborns because their ear canals are too small for consistently accurate readings.
If you obtain an abnormal reading using another method and are unsure what it means, contact your pediatrician rather than delaying medical advice.
- Use a digital thermometer if your baby feels unusually warm or seems unwell.
- For a young infant, obtain a rectal temperature when possible.
- Write down the exact temperature and the time it was measured.
- Note whether your baby is feeding normally and making wet diapers.
- Watch your baby's breathing, alertness, skin color, and overall behavior.
- If the temperature is 100.4°F (38°C) or higher, contact your pediatrician or another medical professional immediately.
What If My Baby Seems Completely Fine?
The recommendation does not change.
A young infant with a confirmed fever can sometimes look surprisingly comfortable—feeding normally, waking appropriately, and appearing alert.
That is reassuring, but it does not eliminate the possibility of an infection.
In babies 3 months old or younger, the fever itself warrants prompt contact with a medical professional. The recommended evaluation depends on the baby's exact age, medical history, examination, and test results.
Could Vaccines Cause a Fever?
Vaccines can sometimes cause fever.
However, because fever in a young infant deserves special attention, parents should still contact their pediatrician if a baby 3 months old or younger develops a temperature of 100.4°F (38°C) or higher after vaccination.
Tell the pediatrician which vaccines were given, when they were given, the exact temperature, how it was measured, and how your baby is behaving.
Should I Give Acetaminophen Before Calling?
Do not delay calling your pediatrician in order to treat the fever first.
In a young infant, determining the cause of the fever is more important than simply lowering the temperature.
Acetaminophen dosing in very young babies should be discussed with your pediatrician. If your pediatrician wants you to give acetaminophen, use the exact dose recommended for your baby's weight and age.
Ibuprofen should not routinely be given to infants younger than 6 months unless specifically directed by a healthcare professional.
When Should I Call My Pediatrician?
If your baby is 3 months old or younger and has a rectal temperature of 100.4°F (38°C) or higher, contact your pediatrician or another medical professional immediately for instructions and prompt medical evaluation.
Do not wait to see whether the fever goes away, rises higher, or additional symptoms develop.
When Should I Seek Emergency Care?
Seek emergency medical care if your baby has fever and also:
- Is extremely sleepy, unresponsive, or very difficult to wake.
- Has trouble breathing or is working hard to breathe.
- Has blue, gray, very pale, or otherwise concerning skin or lip color.
- Is too weak to feed.
- Has repeated vomiting or cannot keep feeds down.
- Has a seizure.
- Shows signs of significant dehydration.
- Develops a sudden purple or bruise-like rash.
- Looks seriously ill to you.
What Might the Doctor Do?
The evaluation depends on your baby's exact age and clinical appearance.
Your pediatrician will examine your baby and may recommend a urine test, blood testing, viral testing, or other studies.
Some infants may need additional testing, observation in the hospital, or antibiotics. Others may be candidates for careful outpatient monitoring depending on their age, examination, and laboratory results.
The American Academy of Pediatrics has specific guidance for evaluating well-appearing febrile infants between 8 and 60 days of age. Management varies according to the infant's age and individual findings.
Frequently Asked Questions
What if the temperature is exactly 100.4°F?
A rectal temperature of exactly 100.4°F (38°C) meets the definition of fever. If your baby is 3 months old or younger, contact your pediatrician or another medical professional immediately.
What if the fever goes back down?
A documented rectal temperature of 100.4°F (38°C) or higher still matters even if the temperature later decreases. Do not assume the problem has resolved simply because the temperature returned to normal.
What if my baby just had vaccines?
Vaccines can cause fever, but a baby 3 months old or younger who develops a temperature of 100.4°F (38°C) or higher should still be discussed promptly with your pediatrician. Tell the doctor when the vaccines were given and how the temperature was measured.
What if my baby feels hot but the thermometer is normal?
Recheck the temperature carefully with an appropriate thermometer. If your newborn is feeding poorly, unusually sleepy, difficult to wake, having trouble breathing, has an abnormal skin color, or simply appears ill, contact your pediatrician even if you have not measured a fever.
One of the most important things for parents to understand is that a young baby with a significant infection may initially look surprisingly well.
That is why the temperature threshold matters. In a baby 3 months old or younger, a rectal temperature of 100.4°F (38°C) or higher deserves prompt medical evaluation even when your baby still seems comfortable.
Clear Answers When You're Caring for a New Baby
Join the Pediatric Parent Guide Parent Club for practical pediatric guidance from Dr. G, newborn resources, and updates when new articles and parent tools are added.
Join the Parent Club →References & Medical Sources
- American Academy of Pediatrics, HealthyChildren.org. Fever and Your Baby
- American Academy of Pediatrics, HealthyChildren.org. How to Take Your Child's Temperature
- American Academy of Pediatrics. Clinical Practice Guideline: Evaluation and Management of Well-Appearing Febrile Infants 8 to 60 Days Old
Related Parent Resources
Find more pediatric guidance about feeding, breathing, skin, diapers, fever, and other common concerns in our Newborn Care Library →
Medical Disclaimer
This article provides general educational information and is not a substitute for medical advice, diagnosis, or treatment from your child's pediatrician or another qualified healthcare professional. Fever in a newborn or young infant can require prompt medical evaluation. If your baby is 3 months old or younger and has a rectal temperature of 100.4°F (38°C) or higher, contact your pediatrician or another medical professional immediately for instructions and prompt medical evaluation. Do not delay seeking medical advice because your baby's temperature decreases or because your baby appears comfortable. If your baby is difficult to wake, has trouble breathing, has a seizure, cannot feed, develops concerning skin color, appears seriously ill, or you believe there is an emergency, seek immediate medical care.