High Fever in Children: What to Do and When to Worry

Almost every parent at some point starts treating the thermometer rather than the child: watching the number, waiting for it to fall, measuring again twenty minutes later. Yet the number is the weakest signal available. A child at 39.5 °C who drinks and plays between peaks is in a better position than a child at 38.2 °C who cannot be roused.

What counts as fever in children and how to measure it

Fever is defined from 38.0 °C measured rectally, or by electronic thermometer in the axilla with a correction. Accuracy differs by method:

More important than the number is the trend and the behaviour. It helps to write down when the fever rose, how high, what was given and what followed: with such a record a doctor sees the picture in a minute.

How to reduce fever in a child: what is allowed and what is not

An antipyretic is given not to normalise a number but to relieve distress: the child should be able to drink, sleep and stop suffering. If a child plays happily at 38.8 °C, there is no reason to intervene.

What to know before opening the medicine cabinet:

• Children are given paracetamol and ibuprofen. The dose is calculated by weight, not by age — the "for ages 3–6" figure on a box is an average and overdoses a slight child. The specific dose is set by the doctor or the package insert.
• Aspirin is contraindicated in children — the risk of Reye syndrome, a severe liver and brain injury.
• Alternating two drugs every couple of hours is a common improvisation that raises the risk of dosing errors; do it only when a doctor has prescribed it.
• Do not sponge with vodka, vinegar or cold water: alcohol is absorbed through the skin, and cold triggers vasoconstriction and shivering that drives the temperature up.
• An antipyretic does not prevent febrile seizures — proven, which means dosing "just in case" achieves nothing.

What always helps: frequent small drinks, light clothing, cool room air. Dehydration during fever is more dangerous than the fever itself — especially with vomiting or diarrhoea.

High fever in children: what to do at 39 °C and above

The number 39 or 40 by itself does not mean severe disease and does not "burn the brain" — in infection thermoregulation is intact and the temperature does not rise without limit. Judge other things:

• How the child looks once the fever comes down. If an hour or two later they revive, drink and respond, that is reassuring even after 39.8 °C.
• Skin colour and periphery. Mottling, a grey tint, cold hands and feet with a hot trunk are worrying.
• Breathing. Rapid, with in-drawing between the ribs, warrants review — see also cough in children.
• Rash. Especially one that does not blanch under pressure — an emergency covered in rash in children.

How long fever lasts in children and when it is too long

In an ordinary viral infection fever lasts 3–5 days. Review is needed when:

• the fever lasts more than 5 days;
• the fever returns after the child had recovered — a typical bacterial complication pattern;
• fever runs without a single other symptom for more than three days — see fever without symptoms.

Febrile seizures in children: what they are and what to do

Febrile seizures occur in 2–5% of children aged 6 months to 5 years, usually as the temperature rises. The child loses consciousness, the body stiffens, limbs jerk rhythmically, the eyes roll up. An episode usually lasts under 2–3 minutes.

What matters: simple febrile seizures do not damage the brain, do not cause epilepsy and do not affect development. They are an age-related feature of an immature brain and are outgrown.

During an episode:

1. Lay the child on their side on a flat surface and clear hard objects away.
2. Note the time — duration matters to the doctor.
3. Put nothing in the mouth: not a spoon, not fingers. The tongue cannot be swallowed, but teeth break.
4. Do not restrain the limbs by force.
5. Call an ambulance if this is the first episode, it lasts over 5 minutes, repeats, involves only one side of the body, or the child stays unresponsive afterwards.

Fever in infants: why under 3 months the rules differ

In the first months of life the immune response is not yet developed, and a serious bacterial infection can run without a single local symptom. Hence the hard rule: 38 °C or above in a child under 3 months means immediate medical assessment, not home observation and not an antipyretic. The same applies in reverse — a temperature below 36 °C with lethargy and feed refusal.

At this age a doctor usually orders testing even when the child looks well: a complete blood count, C-reactive protein and a urinalysis, because urinary tract infection is a common hidden cause of fever in infants.

When to call an ambulance for fever

• a child under 3 months with a temperature of 38 °C or above;
• a seizure lasting over 5 minutes, or a repeat episode;
• a rash that does not blanch under pressure;
• inability to wake the child, confusion, unusual lethargy;
• laboured breathing, chest in-drawing, blue lips;
• the child will not drink, no urine for 8–12 hours, crying without tears;
• bulging fontanelle, neck stiffness, photophobia — see meningococcal disease.

Are blood tests needed for fever in children?

In the first days of a typical viral infection — no. Testing becomes meaningful on day 4–5, when fever returns, when there are no symptoms at all, or in an infant. Usually a complete blood count with differential is taken — paediatric ranges are covered in CBC in children and blood norms by age — plus CRP and ESR, which help separate viral from bacterial inflammation: see inflammation and high-sensitivity CRP and raised ESR. Raised white cells alone do not make a diagnosis — see elevated leukocytes.

This article is informational. Treatment decisions belong to the paediatrician.