What counts as fever

A baby's normal temperature is around 36.5–37.5°C (97.7–99.5°F). Fever is generally defined as a temperature of 38°C (100.4°F) or higher, measured rectally — which is the reliable method for babies, especially under 3 months.

Forehead and ear thermometers are convenient but less reliable for small babies. If the reading seems wrong, confirm with a rectal measurement.

Under 3 months: treat it as urgent

A fever of 38°C or higher in a baby under 3 months requires urgent medical evaluation, even if the baby looks fine. The immune system is still immature, and fever can be the only sign of a serious infection. Call your pediatrician or go to the emergency service without waiting to see if it passes.

Log temperature, medicines and symptoms

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3–6 months and older

  • 3–6 months: a fever of 39°C (102.2°F) or higher is worth a same-day call to the pediatrician, even outside office hours, and any fever should be mentioned at the next visit.
  • 6 months and up: fever alone is less alarming — many viral fevers last 2–3 days. Watch how the baby behaves: alert, drinking, and interested in play are good signs even with a high number.
  • Do not give fever medicine on your own and never give aspirin to a baby or child. Paracetamol or ibuprofen only with the pediatrician's guidance and the correct dose for the child's weight.

Red flags — call the doctor now

  • Fever in a baby under 3 months (38°C or higher).
  • Lethargy: hard to wake, unusually limp, or not interested in anything.
  • Refusing fluids or fewer than 6 wet diapers in 24 hours (dehydration).
  • A rash, especially one that does not fade when pressed.
  • Difficulty breathing, a stiff neck, or a seizure (febrile convulsion).
  • Fever lasting more than 3 days, or any fever that worries you.

What helps at home

1

Comfort over cooling

Dress the baby lightly, keep the room comfortable, offer fluids often. Do not use cold baths or rubbing alcohol — they do more harm than good.

2

Medicines only with guidance

If the pediatrician approved it, dose strictly by weight. Never alternate doses on your own and never give aspirin.

3

Watch the behavior, not just the number

A lively baby with 38.5°C is usually less worrying than a limp baby with 38°C. Log temperature, fluids, and diaper output — patterns help the doctor.

4

Know when it is not fever

After vaccines, mild temperature elevation for 24–48 hours is common. A too-warm room or too many layers can also push the number up.

Track it so the doctor can see it

Logging temperature, medicines, fluids, and wet diapers turns a stressful week into clear data: "Fever started Tuesday, peaked at 39.2 on Wednesday evening, 3 wet diapers per day since." That record is exactly what a pediatrician needs — and it calms you down to have it.

Disclaimer: This article is for general guidance and does not replace medical advice. Fever in a baby under 3 months, or any red flag listed above, means contacting a doctor immediately.