Fever in a baby is one of the most common reasons parents call us. The number on the thermometer matters less than two other things: how old your child is, and how they look. A young infant with any fever is different from a toddler with a 103. This handout covers what counts as a fever, which ages and findings are urgent, how to treat for comfort, and when to pick up the phone.
Key Takeaways
- Fever is defined as a temperature of 100.4°F (38°C) or higher.
- Under 3 months: any rectal temperature of 100.4°F or higher, or signs that your infant looks ill, is inconsolable, is feeding poorly, or seems unusually sleepy, is urgent. Call us immediately, and use the emergency department if it is after hours.
- For older infants and children, how your child looks matters as much as the number. A child who is drinking, interacting, and smiling between spikes is usually safer than the thermometer suggests.
- Treat fever for comfort, not to chase a specific number.
- Never give aspirin to a child with a fever because of the risk of Reye syndrome.
What Counts as a Fever
A fever is a rectal, oral, forehead (temporal artery), or ear temperature of 100.4°F (38°C) or higher. Axillary (armpit) readings run about a degree lower and are less reliable for confirming a fever in a young infant.
Body temperature normally varies by about a degree across the day, trending higher in the late afternoon. A brief reading in the high-99 range in an otherwise well child usually reflects that normal rhythm.
Age-Based Quick Reference
Under 3 months.
Any rectal temperature of 100.4°F or higher, or signs that your infant looks ill, is inconsolable, is feeding poorly, or seems unusually sleepy, can be the first sign of a serious infection in this age group and needs to be evaluated by a clinician right away. Call the office immediately. If we are closed, take your infant to the nearest pediatric emergency department. Do not give acetaminophen, ibuprofen, or any other fever or pain medication at home until your infant has been evaluated.
3 months to 2 years.
Call us the same day for any fever that is 102°F or higher, any fever that lasts more than 24 hours without a clear source (cough, congestion, ear pulling, rash, vomiting), and any fever of 104°F or higher at any point. At this age, how the child looks is a key part of the assessment.
Over 2 years.
Call us for fever that persists beyond 3 days, fever of 104°F or higher, or any fever in a child who looks unusually ill, is drinking poorly, or is showing any of the red flags below.
Red Flags: Go to the Emergency Department
- Any fever in an infant under 3 months.
- A stiff neck, persistent severe headache, or confusion.
- In infants, watch for a bulging soft spot, an unusually high-pitched cry, or fussiness that gets worse when you pick the baby up. Meningitis in young infants often does not show classic neck stiffness.
- Purple or bruise-like spots, or a rash that does not fade when pressed (non-blanching).
- Labored breathing, retractions, or blue lips or skin.
- Limpness, unresponsiveness, or inability to be roused.
- A seizure.
- Severe abdominal pain or vomiting that will not stop.
- Signs of significant dehydration: no urine for 8 or more hours in an infant or 12 or more hours in an older child, no tears, sunken eyes, dry mouth.
Why Fevers Happen
Fever is the body’s response to infection, not the infection itself. It is part of how the immune system fights viruses and bacteria, and the height of the fever does not reliably tell us how serious the underlying illness is. Most childhood fevers come from common viral infections. Other common causes include ear infections, urinary tract infections, and streptococcal pharyngitis. A mild low-grade fever in the day or two after routine vaccinations is expected and reflects a healthy immune response. Routine immunizations, including pneumococcal, Hib, influenza, COVID, and RSV protection through maternal Abrysvo at 32 to 36 weeks of pregnancy or infant nirsevimab, reduce the risk of the most dangerous febrile illnesses in this age group. In Florida, fever-causing respiratory viruses circulate year-round, not just in winter.
Taking a Temperature
- Rectal: most accurate, especially in infants under 3 months. Use a digital thermometer and a small amount of lubricant.
- Temporal artery (forehead): quick and accurate in children 3 months and older. Follow the device instructions carefully.
- Tympanic (ear): reasonable for children 6 months and older. Not used in newborns.
- Oral: useable in cooperative children around age 4 and up.
- Axillary (armpit): least reliable. Can be used as a screen, but confirm a positive reading with a more reliable method.
Use a digital thermometer. Do not use mercury glass thermometers.
Treating for Comfort at Home
- Offer frequent fluids. Breast milk or formula for infants under 6 months. Older children can also have water or an oral electrolyte solution. For mild dehydration, half-strength apple juice is an acceptable alternative.
- Dress lightly. Overbundling traps heat and pushes the temperature higher.
- Keep the room comfortably cool.
- Use a lukewarm sponge bath only for comfort. Cold water baths are not recommended because the shivering they trigger raises temperature.
- Acetaminophen (Tylenol) and ibuprofen (Motrin, Advil) are not for home use in infants under three months of age, who must be seen first. For infants three months and older, acetaminophen can be dosed by weight. Ibuprofen can be used from six months of age and is also dosed by weight. We are happy to help you confirm the dose.
- Do not use aspirin in any child with a fever because of the risk of Reye syndrome.
- Do not alternate acetaminophen and ibuprofen routinely without pediatric guidance. In most cases, one medication at the correct dose is all that is needed.
Febrile Seizures
Febrile seizures occur in about 2 to 5 percent of children between 6 months and 5 years of age. They are frightening to watch, but simple febrile seizures are almost always benign, do not cause brain damage, and do not mean your child has epilepsy. A simple febrile seizure is generalized, lasts less than 15 minutes, ends on its own, and does not recur within 24 hours. Call 911 if a seizure lasts longer than 5 minutes, if a second seizure occurs before recovery, or if your child does not return to normal afterward. Any first seizure warrants same-day evaluation.
Preventing Dehydration
- Infants under 6 months: breast milk or formula only. No plain water.
- Infants 6 to 12 months: breast milk or formula plus small amounts of water between feeds.
- Children over 12 months: water, milk, or an oral electrolyte solution if intake of solids is reduced.
- Track wet diapers or trips to the bathroom. Fewer than half the usual number of wet diapers in a 24-hour period in a young child is a warning sign.
Bottom Line
Fever is a symptom, not the disease. In a young infant, the number alone is enough to act on. In older children, how your child looks and how they are acting matters more than the reading. When in doubt, call us. We would rather hear from you early than late.
Call ELP at (727) 372-6760 or schedule online. Stay healthy my friends.
Sources
- American Academy of Pediatrics, HealthyChildren.org: fever and fever management articles.
- AAP Clinical Practice Guideline: Evaluation and Management of Well-Appearing Febrile Infants 8 to 60 Days Old (2021). ELP extends the under-3-month rule to the full 0 to 90 day range based on residual occult bacterial infection risk in that age band.
- AAP Clinical Report: Fever and Antipyretic Use in Children.
- AAP Clinical Practice Guideline: Febrile Seizures.
- Seattle Children’s / Schmitt Pediatric Guidelines: Fever.
