High Fever in Kids: When to Worry

Two numbers in pediatrics are absolute, and everything between them is judgment. The American Academy of Pediatrics says call immediately for a baby younger than 3 months (12 weeks) with 100.4 °F (38.0 °C) or higher, and call for a temperature repeatedly above 104 °F (40 °C) at any age. Outside those, how your child looks and acts is the better signal than the thermometer.

Age is the first question, not the temperature

Age	What the number does
Younger than 3 months	100.4 °F (38.0 °C) is itself the reason to call, alone
3 to 12 months	MedlinePlus sets a contact threshold at 102.2 °F (39 °C) or higher
Older than 12 months	The number matters less; behavior and duration lead
Any age	Repeatedly above 104 °F (40 °C) — call

The reason for the split is not that fever is more dangerous in a newborn. It is that a newborn cannot show you they are sick in any of the usual ways, and the rate of serious bacterial infection behind fever is highest in that window. See fever in a baby: what to do.

Behavior is the signal that outranks the number

A child running 103 °F who is playing between peaks, drinking, and making eye contact is a different situation from a child at 101 °F who is limp and unreachable. The AAP’s own warning list is mostly about behavior and about symptoms other than heat. Call if the child:

Looks very ill, is unusually drowsy, or is very fussy.
Has a stiff neck or a severe headache.
Has breathing problems.
Has an unexplained rash.
Has repeated vomiting or diarrhea.
Has throat pain or ear pain.
Has been exposed to extreme heat.
Has an immune system condition, a heart problem, or has had seizures before.

MedlinePlus adds a 911 list: inconsolable crying, unresponsiveness or confusion, inability to walk, blue lips, tongue or nails, inability to move a limb, or a seizure.

The duration rules

The AAP puts the limit at more than 24 hours for a child under 2, and more than 72 hours for an older child. MedlinePlus is slightly wider — 24 to 48 hours under 2, 48 to 72 hours over — and adds fevers that come and go over a week or more. Either way, a fever that has outstayed the usual viral window is a reason to be seen, independent of how high it is.

Febrile seizures, and what the evidence says

They happen in 2% to 5% of US and European children, per StatPearls, typically between 6 months and 5 years, peaking at 12 to 18 months. About 30% of affected children have more than one.

The prognosis is far better than the experience suggests. Simple febrile seizures carry roughly a 1% to 2% risk of later epilepsy, against 0.5% to 0.9% in the general population — a difference smaller than most parents assume. StatPearls states febrile seizures are typically harmless and do not cause long-term neurological or cognitive problems, and that a single episode is not linked to learning disability, lower intelligence, or behavioral problems.

The part worth acting on: antipyretics have not been shown to prevent recurrence, and neither have non-drug cooling methods. Giving medicine at the first hint of fever to head off a seizure does not work. A first seizure still needs medical evaluation to confirm what it was.

What to do while you watch

Offer fluids often. Dehydration is the realistic risk, not the temperature.
One layer, not three. The AAP says do not overdress; a single layer, plus a blanket if the child is shivering.
Skip the cold bath and the alcohol rub. The AAP calls them no longer recommended and says they can have adverse effects.
Medicate for discomfort, not for a number. Dose by weight; ibuprofen is not for infants under 6 months; aspirin is for adults only.
Watch the trend, not the peak. A child improving over a day at 102 °F is doing better than a child worsening at 100.6 °F.

For the mechanism and the wider list of causes, see fever causes. For a fever that lingers just above the line for days, see low grade fever causes. For the conversion between scales, see fever: Fahrenheit to Celsius.

This content is informational and does not replace medical evaluation, diagnosis, or treatment.

Frequently asked questions

At what temperature should I call the doctor for my child?

The AAP gives two numbers: 100.4 °F (38.0 °C) for a baby younger than 3 months, and a temperature repeatedly above 104 °F (40 °C) at any age. Between those, how the child looks and behaves decides.

Does a higher fever mean a worse infection?

Not reliably. A mild virus can run 103 °F and something serious can sit at 100.5 °F. The exception is age: in the first three months of life, the number alone triggers evaluation.

Do fever reducers prevent febrile seizures?

No. StatPearls states plainly that antipyretics have not been shown to prevent recurrence of febrile seizures, and neither have non-drug cooling methods.

How long can a child's fever last before I should call?

The AAP sets it at more than 24 hours in a child under 2, and more than 72 hours in an older child. MedlinePlus uses a similar 24 to 48 hour and 48 to 72 hour split.

Should I wake a sleeping child to give fever medicine?

Generally no. Sleep is doing more for the illness than a lower number would. Fever reducers exist for comfort, and a child comfortable enough to sleep is already there.

Sources

Written by Lucas Silva · Reviewed by Lucas Silva · Updated on August 14, 2026