Fever in Children: What the Number Means, and What Actually Matters

Under one month old: any fever is an emergency

A rectal temperature of 100.4°F (38°C) or higher in a baby under one month means call us immediately or go to an emergency room, at any hour. Even if they seem well. Even if it is the middle of the night.

A young baby cannot contain an infection the way an older child can, so a fever may be the only sign of something serious and it needs assessment within hours. Do not give fever medicine and wait to see how they are in the morning. Use a rectal thermometer — forehead and ear readings are not reliable at this age.

For every child older than that, here is the sentence this whole page exists to deliver: how your child looks and behaves matters more than the number on the thermometer.

A child with a temperature of 103°F who is drinking, playing between naps, and recognisable as themselves is usually less worrying than a child at 100.8°F who is limp, refusing fluids, and not responding to you. The height of a fever does not tell you how serious the illness is.

What a fever actually is

It is the immune system turning up the thermostat on purpose, because many viruses and bacteria replicate less efficiently at higher temperatures. The fever is the response, not the disease.

Two things follow, and both surprise people:

Treating a fever makes a child more comfortable. It does not shorten the illness and it does not treat the cause. That is a perfectly good reason to give medicine — a comfortable child drinks and rests, which genuinely helps — but it is not a cure and there is no need to chase a normal number.

And a fever itself, at the temperatures children actually run, does not cause brain damage. That fear drives an enormous amount of night-time worry. Ordinary infectious fevers do not reach the range where heat injures tissue. What matters is what is causing it.

When to call us

Regardless of the number:

• Any fever under one month — see the top of this page
• Under six months, a fever above 102°F, or any fever with poor feeding, unusual sleepiness, or persistent irritability
• A fever lasting more than three days, or one that goes away and then returns
• A child who will not drink, or who has not passed urine in eight hours
• Ear pain, a sore throat with no cough or runny nose, painful urination, or a new rash
• A child who seems much worse than the illness explains
• Any fever in a child with a serious chronic condition, a weakened immune system, or a recent hospital stay
• You are worried and cannot say why. That is a good enough reason. Parental instinct about a child’s illness is a genuinely useful clinical signal.

Go to an emergency room or call 911 for

• A stiff neck, or a child who cries when you flex their chin to their chest
• A rash of small dark red or purple spots that do NOT fade when you press on them
• Difficulty breathing, or breathing that looks like hard work
• A child who cannot be woken properly, or is confused
• A seizure lasting more than five minutes, or one followed by no return to normal
• Persistent vomiting, or an inability to keep any fluid down
• Blue or grey lips
• Severe headache with light sensitivity
• Any fever in a baby under one month

What helps at home

Fluids, before anything else. Small amounts often. Water, milk, oral rehydration solution, ice lollies — whatever they will take. Dehydration is the complication you are actually preventing.

Medicine for comfort, not for the number. Acetaminophen, or ibuprofen for children over six months, dosed by weight rather than by age — a child at the light end of their age band gets too much from an age-based dose. If you are unsure of the dose, call and ask; we would much rather answer that than have you guess. Out of hours, a pharmacist can check a weight-based dose with you — and if you think a child has had too much of anything, Poison Control answers at any hour on 1-800-222-1222.

Never aspirin for a child or teenager, because of the risk of Reye syndrome.

Do not wake a sleeping child to medicate them. Sleep is doing more good than the dose would.

Dress them normally and keep the room comfortable. Bundling a feverish child up traps heat; stripping them and running a fan causes shivering, which raises temperature. No cold baths, and never an alcohol rub — alcohol is absorbed through the skin and is genuinely dangerous.

Let them eat what they want and rest as much as they want. Appetite returns after the fever does.

Febrile seizures, because they are terrifying and usually harmless

Some young children have a seizure when their temperature rises quickly. It is one of the most frightening things a parent will witness and, in the common form, it does not cause lasting harm and does not mean the child has epilepsy.

If it happens: put them on their side on a soft flat surface, clear the space around them, do not put anything in their mouth, do not try to restrain them, and note the time. Call 911 if it lasts more than five minutes, if it happens more than once in a day, if they do not return to themselves afterwards, or if it is their first one and you have not been told what to expect.

Fever medicine does not prevent febrile seizures, so there is no reason to medicate on a schedule hoping to avoid one.

Two things that are not fever

Teething does not cause a real fever. It can raise a temperature slightly — a tenth or two — and a genuinely feverish teething baby is a baby with something else going on. Attributing a 102°F to teeth is how an ear infection gets missed for three days.

And the Arizona one, which matters more here than almost anywhere. A child who has been outside in summer can have a high body temperature from the environment rather than from infection, and the two need completely different responses.

Heat illness looks different: it comes on during or shortly after heat exposure, with flushed skin, headache, nausea, cramps, and either heavy sweating or — in the dangerous form — hot, dry skin with no sweating at all, plus confusion or unsteadiness. That is heat stroke and it is a 911 emergency: move them into shade or air conditioning, cool them with water and airflow, and call. Do not give fever medicine for heat illness; it does not help and it delays the thing that does.

If your child has just come in from playing outside and is hot, cool them down first and take their temperature again after twenty minutes in the air conditioning before deciding what you are dealing with. Our guide to heat safety in Arizona covers the rest.

Taking a temperature, briefly

Rectal is the accurate one and is what any threshold on this page refers to, particularly under three months. Oral works from around four or five years. Armpit is a rough screen — useful for “is there a fever at all”, not for a number you act on. Forehead and ear thermometers are convenient and less reliable, especially in babies; they are fine for tracking a trend in an older child and not for a decision under three months.

Add nothing to the reading and subtract nothing from it. And remember that a normal temperature in a child who is clearly unwell is also worth a call — very young babies and seriously ill children can run a low temperature rather than a high one, and that is not reassuring.

Sources

1. Fever — MedlinePlus Medical Encyclopedia, U.S. National Library of Medicine. https://medlineplus.gov/ency/article/003090.htm
20. Fever and Your Baby — American Academy of Pediatrics, HealthyChildren.org. https://www.healthychildren.org/English/health-issues/conditions/fever/Pages/Fever-and-Your-Baby.aspx

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