Infant Fever

Overview

An infant fever is a body temperature that is higher than normal, generally defined as 100.4°F (38°C) or above when measured rectally. A fever is not an illness itself but a sign that the body is responding to something, most often an infection. In babies, fever is taken very seriously because their immune systems are still developing and they cannot tell you how they feel.

How worried to be depends heavily on the baby's age. In a newborn or young infant, even a mild fever can be the first and only sign of a serious infection and is treated as a medical emergency. In older babies, fever is more often due to common viral illnesses and is managed at home, with attention to comfort, hydration, and warning signs. Knowing the age-based rules is the most important thing for caregivers.

Common Causes

Most fevers in babies are caused by infections the body is fighting:

• Viral infections: Colds, the flu, roseola, and other common viruses are the leading cause.
• Ear infections: Otitis media, often after a cold.
• Respiratory infections: Bronchiolitis, croup, or RSV.
• Gastrointestinal infections: Stomach bugs such as gastroenteritis.
• Other infections: Urinary tract infections and, less commonly, more serious bacterial infections.
• After vaccines: A mild, short-lived fever can follow some immunizations.

Overbundling can also raise a baby's temperature, so check after removing extra layers.

Associated Symptoms

Fever often comes with other symptoms that help identify the cause:

• Fussiness, an irritable infant, or crying
• Poor feeding (loss of appetite) or feeding problems
• Runny nose, cough, or congestion
• Vomiting, diarrhea, or a rash
• Sleepiness or sleep problems

Warning signs that need urgent care include a rash that does not fade when pressed, difficulty breathing, a stiff neck, a bulging soft spot, a seizure, or being very hard to wake.

Diagnosis & Evaluation

How a fever is evaluated depends on the baby's age and how they look:

• Temperature measurement: A rectal thermometer is the most accurate for infants.
• History and exam: Reviewing symptoms, feeding, and behavior, and examining the ears, throat, chest, and skin.
• Tests for young infants: Babies under about 3 months with fever often need blood, urine, and sometimes spinal fluid tests to rule out serious infection.

Older, well-appearing babies with an obvious viral cause may need no tests at all.

Treatment & Management

For older babies with a mild illness, fever care focuses on comfort and hydration:

• Fluids: Continue breast milk or formula frequently to prevent dehydration.
• Comfort: Dress the baby lightly and keep the room comfortably cool.
• Fever-reducing medicine: Acetaminophen (for babies over a certain age) or ibuprofen (only for babies 6 months and older) at the correct dose for weight, given as directed by your pediatrician. Never give aspirin to children.
• Treat the cause: Such as antibiotics for a confirmed bacterial infection.

The goal is comfort, not necessarily a normal temperature. Always confirm dosing with your pediatrician, especially for young infants.

Self-Care & Prevention

You can lower the chance of the infections that cause fever:

• Keep vaccines up to date, which protect against many serious infections.
• Wash hands often and ask others to do so before holding your baby.
• Limit exposure to sick contacts, especially for newborns.
• Breastfeed if possible, which helps protect against some infections.
• Avoid overbundling, which can raise a baby's temperature.

Always have a reliable thermometer at home and know that any fever in a baby under 3 months needs prompt medical attention.

When to See a Doctor

Call your doctor or seek emergency care for an infant with fever if:

• Your baby is under 3 months and has any fever of 100.4°F (38°C) or higher — this is always urgent
• Your baby has trouble breathing, looks blue, or breathes very fast
• There is a rash that does not fade when pressed with a glass, a stiff neck, or a bulging soft spot
• Your baby has a seizure, is very hard to wake, or is unusually floppy
• The fever is very high, lasts more than a couple of days, or your baby shows signs of dehydration (few wet diapers, dry mouth, no tears)

When in doubt about a feverish baby, especially a very young one, seek medical advice promptly.

Related Topics

Frequently Asked Questions

References

1. American Academy of Pediatrics. Fever in infants and children.
2. Centers for Disease Control and Prevention (CDC). When your child is sick.
3. MedlinePlus, U.S. National Library of Medicine. Fever.
4. Mayo Clinic. Fever in babies and toddlers.