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A fever is technically a sign the immune system is responding to something, and on its own it isn't always cause for alarm in an older baby — but the right response depends heavily on your baby's age.
What counts as a fever
Generally, a rectal temperature of 100.4°F (38°C) or higher is considered a fever in babies. Rectal thermometers are typically the most accurate for infants, though your pediatrician can advise on the best method for your baby's age.
Fever guidance by age
| Age | General guidance |
|---|---|
| Under 3 months | Call your pediatrician immediately for any fever — this age group needs prompt evaluation |
| 3-6 months | Call for a fever over 102°F (38.9°C), or sooner if your baby seems unwell |
| 6+ months | Generally call for a fever over 104°F (40°C), or sooner based on how your baby is acting |
These are general benchmarks — always follow your own pediatrician's specific guidance for your baby.
How your baby is acting matters as much as the number
A baby who is alert, drinking fluids, and consolable with a moderate fever is generally in a different situation than a baby with a lower fever who is lethargic or difficult to console — behavior is an important piece of the picture, not just the thermometer reading.
Managing a fever at home
- Dress baby lightly — overbundling can trap heat.
- Offer fluids regularly to prevent dehydration.
- Age-appropriate fever reducer, only as directed by your pediatrician.
- Never give aspirin to a baby or child due to the risk of Reye's syndrome.
When to seek care right away
- Any fever in a baby under 3 months old.
- Difficulty breathing, unusual lethargy, or trouble waking.
- A fever accompanied by a rash, stiff neck, or repeated vomiting.
- Signs of dehydration — fewer wet diapers, dry mouth, no tears.
- A fever that lasts more than a couple of days.
