Fever in children: what actually matters

Almost every parent who calls us about a fever opens with a number. 103.2. 101.8. Whatever the forehead thermometer said at 2am. And almost every time, the number is not the thing that decides what happens next.

Fever is the immune system doing its job. The height of a fever correlates poorly with how serious the underlying illness is. A child with a nasty virus can run 104 F and be fine by Thursday. A child with a serious bacterial infection can run 100.8 F and need admitting. What tells us which is which is how the child looks, how old they are, and how long it has gone on.

The one situation where the number is everything

A rectal temperature of 100.4 F or 38 C or higher in a baby under three months old is a medical emergency evaluation. Not a clinic visit tomorrow. Not a dose of acetaminophen and a recheck. Young infants have immature immune systems and can have a serious bacterial infection with almost no other signs, so the standard of care is a full evaluation, usually including blood and urine testing and often a lumbar puncture.

If your baby is under three months and has any fever, go to a pediatric emergency department and call us on the way. Do not give fever medicine first, because it masks the picture the team needs to see.

What we actually assess after three months

• How your child looks between fevers, once the medicine has brought the temperature down. A child who perks up and plays is reassuring. A child who stays listless is not.
• Hydration. Wet nappies, tears, moist lips and a normal weight against the last recorded weight matter far more than the thermometer.
• Work of breathing. Fast breathing, nostril flaring, grunting, or the skin pulling in between the ribs needs to be seen now.
• Duration and pattern. A fever past five days, or a fever that resolves for a day and then returns, changes the differential.
• Rash. Any rash of purple or red spots that does not fade when you press a clear glass against it is a 911 call.

Why we treat for comfort, not for a target

There is no evidence that bringing a temperature down prevents febrile seizures or shortens the illness. We medicate so that a child will drink, sleep and be comfortable. If your child is at 102 F, drinking, weeing and watching television, you do not need to reach for anything.

When you do medicate, dose by weight rather than by age, and use a weight measured in the last three months. The most common preventable dosing error we see is a dose calculated from a weight the child had last winter.

Alternating medicines

Alternating acetaminophen and ibuprofen on a timer is where families end up double dosing at 4am. If your child genuinely needs both, write down the drug, the dose and the time on a piece of paper on the kitchen counter, and call us. Do not run the schedule from memory.

Ibuprofen is not for babies under six months, and it is a poor choice in a child who is vomiting or dehydrated because it is hard on the kidneys in that setting.

When to call us

• Any fever in a baby under three months, which is an emergency department visit
• Fever lasting more than five days at any age
• Fever that goes away for a day and comes back
• A child who is not drinking, or who has had no wet nappy for eight hours
• A child who looks worse to you even though the temperature has come down

And if your child is struggling to breathe, unresponsive, having a seizure, or has a rash of purple spots that does not blanch, do not call us. Call 911.

If this is a medical emergency, or your child is struggling to breathe, unresponsive, having a seizure, or badly injured, call 911 now. Call 911.

General information, not medical advice. It is not tailored to your child and it does not replace a visit. Guidance changes. This article was last reviewed on the date shown above.