The first time you see a high temperature on a thermometer in a small child, the instinct is alarm. Fever is one of the top reasons parents call NHS 111, attend A&E, or take a child to urgent care — and most of those visits, while completely understandable, end with the same answer: it's a viral infection, the temperature is the body doing its job, and you can manage it at home.
The reason this article exists isn't to tell you fever is harmless. It's to give you the framework that paediatricians actually use: which fevers are routine, which need same-day assessment, which need an ambulance now, and what's actually worth doing in the meantime. The single most useful shift for parents is moving away from "what number does the thermometer say?" to "how is the child in front of me?" — because that's the variable that actually predicts how worried to be. A child with a 40°C temperature who is drinking, looking at you, and grumbling at being made to lie down is much less concerning than a child at 38.5°C who is listless and floppy.
Logging temperature readings, the timing of doses, and the pattern of symptoms in Healthbooq gives you accurate information when you call NHS 111 or speak to your GP — and helps tell whether a fever is genuinely persistent or fluctuating with medication.
What Fever Actually Is
Fever — body temperature above 38°C — is not the illness. It's the body's response to the illness. When the immune system detects a pathogen (most often a virus), the hypothalamus raises the body's set-point temperature. This serves two purposes: many viruses and bacteria replicate less efficiently at higher temperatures, and several arms of the immune response work better when the body is warm.
This has practical implications:
- Treating the fever doesn't treat the illness. Paracetamol and ibuprofen reduce temperature and discomfort. They don't shorten the illness or kill the bug.
- There's no specific temperature that's dangerous in itself. The brain's thermostat won't allow body temperature to climb to genuinely harmful levels (over about 41.5°C) from infection alone. Heat-related illness from external heat (heatstroke) is different and dangerous; infection-driven fever is regulated.
- The number on the thermometer is just one data point. A 39.8°C fever in a child who's drinking, alert, and engaging is much less worrying than a 38.5°C fever in a child who's lethargic and refusing fluids.
The aim of fever management isn't to drive the temperature down to "normal". It's to make the child comfortable enough to drink, sleep, and rest while their immune system does its work.
Measuring Temperature Properly
Different methods, different accuracy:
- Digital underarm (axillary) thermometer. Reasonably accurate for under-fives. Reads 0.3–0.5°C lower than core. NICE recommends this method for under-fives. Hold the arm down against the body for the recommended time.
- Digital tympanic (ear) thermometer. Quick and useful in older babies and children. Less reliable in babies under 3 months (small ear canal). Quality varies by brand; cheaper ones are less reliable.
- Forehead infrared thermometer. The "non-contact" type. Useful for screening but vary by quality; can be affected by sweat, hair, and ambient temperature. Confirm a fever reading with another method.
- Rectal thermometer. Most accurate but rarely needed at home. Used in some clinical settings.
- Forehead strips. Not reliable enough — don't use them.
You don't need a fancy thermometer; a basic digital one from any pharmacy is fine. What you do need is to use the same one consistently so readings are comparable, and to know roughly how to interpret the result based on the method.
A fever is generally:
- 37.5°C or above (under-arm)
- 38°C or above (oral, tympanic, rectal)
In practice, most paediatric guidelines work to 38°C as the threshold.
Under Three Months: A Different Rule
This is the single most important thing in this article. A baby under three months with a temperature of 38°C or higher needs same-day medical assessment, every time.
Not "see how they look first". Not "give some Calpol and see if it comes down". Not "wait until tomorrow". Same-day assessment, every time. Call NHS 111 or your GP, or go to A&E.
The reasons:
- The immune system in very young babies is immature; bacterial infections can progress quickly.
- Clinical signs of serious infection are less obvious in newborns than in older children.
- Conditions that need urgent treatment — sepsis, meningitis, urinary tract infection, pneumonia — can present in babies this young with little more than fever and reduced feeding.
- Standards (NICE NG143, AAP) all recommend hospital assessment for fever in this age group, often including blood tests, urine sample, and sometimes a lumbar puncture.
This isn't about overreaction. It's about a window where the cost of delay can be high and the cost of assessment is low. By 3 months, when the immune system has matured and routine vaccinations have started, the rules become more like older children — but until then, fever is a same-day medical event.
3–6 Months: Caution, Not Panic
Babies between 3 and 6 months with fever should be assessed by a GP or NHS 111 if the temperature is 39°C or above, or if there are any other concerning features. Fever in this group is more often a routine viral illness than serious bacterial infection, but the threshold to seek advice is still lower than for older children.
Over Six Months: The Standard Framework
For children over 6 months, fever is most often a self-limiting viral illness — colds, hand-foot-and-mouth, croup, gastroenteritis, ear infections, urinary tract infections, and a long list of other ordinary childhood viruses. Most can be managed at home with comfort measures, fluids, and time.
The standard NICE framework uses a "traffic light" system based on the child's overall appearance, not the temperature:
Green (low risk) — usually viral, manage at home:- Normal colour
- Responds normally; smiles
- Stays awake, content, alert
- Strong normal cry, or not crying
- Normal skin and eyes; moist mouth
- Pallor (paleness)
- Not responding normally to social cues
- Wakes only with prolonged stimulation
- Decreased activity, no smile
- Reduced fluid intake
- Dry mucous membranes
- Reduced urine output (dry nappies for 8+ hours)
- Persistently high temperature ≥39°C in 3–6 month olds
- Fever lasting 5 days or more
- Rigors (shaking chills)
- Swollen joint or limb that the child won't use
- Pale, mottled, blue, or grey skin
- No response to social cues
- Appears very ill to a healthcare professional
- Doesn't wake or stay awake
- Weak, high-pitched, or continuous cry
- Grunting, very fast breathing, or marked indrawing of chest
- Reduced skin elasticity (sign of significant dehydration)
- Bulging fontanelle (the soft spot)
- Non-blanching rash
- Stiff neck
- Status epilepticus (seizure that doesn't stop or recurs)
- Focal neurological signs
- Focal seizures (limited to one side)
The key clinical move: look at the child, not the thermometer. A bright-eyed child who is grumpy but engaged is doing the right thing with their fever. A floppy, unresponsive child needs assessment regardless of what the thermometer says.
How To Manage Fever At Home
For most children, the work is comfort, hydration, and observation:
Medications. Paracetamol or ibuprofen for discomfort, not "to bring the fever down". The aim is the child's comfort, not a normal-looking thermometer. If a child is feverish but happy, no medication is needed. If they're feverish and miserable, treat the misery.
- Paracetamol (Calpol/Disprol/branded paediatric paracetamol):
- Ibuprofen (Nurofen for children/Calprofen):
Don't alternate paracetamol and ibuprofen as a routine pattern — current NICE guidance is to use one medication first, and only consider switching to or alternating with the other if the child is still distressed despite the first. Alternating both routinely doesn't reduce illness duration and increases the risk of dosing errors.
Hydration. Offer fluids frequently — small amounts often. For babies, breastfeeding or formula on demand. For older children, water, milk, dilute squash, or oral rehydration solution (Dioralyte) if vomiting or significant fever. Look for adequate wet nappies/urine output.
Light clothing. A thin layer is enough; over-bundling traps heat. The cosy-cardigan instinct works against the body's effort to lose heat.
Cool environment. A normal room temperature is fine. Don't bake the room.
Don't tepid-sponge. Older advice that's been dropped — it makes children shiver (which raises the temperature) and is distressing.
Rest. Sick children don't need to be in bed; they need to be allowed to do as little as they want. Most will tell you what they need.
When To Seek Help, Specifically
Call 999 or go to A&E now if:
- Non-blanching rash (a rash that doesn't fade when you press the side of a glass against it) anywhere on the body in a feverish child
- Difficulty breathing — fast breathing, laboured breathing, indrawing of the chest under the ribs, blue around the lips
- Cannot rouse them, or unusually sleepy and unresponsive
- Floppy, lifeless
- High-pitched, weak, or continuous cry
- Stiff neck or photophobia (turning away from bright light)
- Bulging fontanelle in a baby
- A seizure that's lasting more than 5 minutes, or a child that doesn't recover normally afterwards
- Significant dehydration: very dry mouth, no tears, sunken eyes, fewer than half the normal wet nappies
Call NHS 111 (or speak to your GP same-day) if:
- Fever in a baby under 3 months, any temperature
- Fever 39°C or above in a 3–6 month old
- Fever lasting 5 days or more
- Fever that returns after the child seemed to be getting better
- Reduced fluid intake or wet nappies but not severely dehydrated
- Persistent vomiting
- Concerns about an unwell child even without specific red flags — your instinct that something isn't right is data
- Pre-existing condition (immunocompromised, sickle cell, congenital heart disease, etc.) where the threshold for assessment is lower
For everything else — including a child who is feverish but drinking, alert, playful enough — home management is fine.
Things Parents Worry About That Aren't Usually The Problem
- The number itself. 40°C in an otherwise well child is not more dangerous than 38.5°C in the same child. Brain damage from fever from infection alone is essentially never seen in well children — it's the underlying infection (e.g., meningitis), not the temperature, that causes harm.
- Febrile convulsions. Around 1 in 20 children between 6 months and 5 years will have a febrile convulsion at some point. They look frightening — generalised stiffening or jerking lasting up to 5 minutes — but the simple ones (under 15 minutes, generalised, recovers fully) don't cause brain damage and don't predict epilepsy. Stay calm, lay the child on their side, time it. Call 999 if it lasts more than 5 minutes, recurs, or the child doesn't recover normally.
- Sweating. Sweating is the body cooling itself; it's a sign the temperature is coming down, not a problem.
- Cold hands and feet with a hot trunk. This is the body conserving heat for the core. Common at the start of a fever, not a danger sign by itself.
- Shivering. When the temperature is rising, the body shivers to make heat. Wrapping the child does not help; the body is just resetting upwards. The shivering will stop as the new set-point is reached.
- Teething doesn't cause fevers above 38°C. A teething child can have a slight rise in temperature, but a true fever is from infection, not teeth. If a teething child has a temperature above 38°C, treat it as a fever — don't write it off as teething.
What Actually Causes Fevers in Children
Most fevers in children are viral — usually one of the dozens of viruses that circulate around nurseries and schools. The most common include:
- Common cold viruses (rhinovirus, coronavirus types, respiratory syncytial virus)
- Influenza
- Croup (parainfluenza)
- Hand-foot-and-mouth disease (coxsackievirus)
- Roseola (HHV-6) — high fever for 3–5 days, then a fine pink rash as the fever resolves
- COVID-19
- Adenovirus (often with conjunctivitis or sore throat)
- Norovirus and rotavirus (gastroenteritis)
- Tonsillitis (often viral, sometimes streptococcal)
- Ear infections (usually viral, sometimes bacterial)
Bacterial infections are less common but include:
- Urinary tract infections (commoner than people realise; can present with just fever in young children)
- Pneumonia
- Bacterial tonsillitis (group A strep)
- Meningitis (rare, urgent)
- Cellulitis or skin abscess
A fever without obvious source (no cough, no rash, no diarrhoea, no obvious clue) in a child under 5 sometimes warrants a urine test — UTIs in young children often present with fever alone.
After the Fever
Most viral fevers resolve in 3–5 days. The post-fever period can include:
- Continued tiredness for several days
- Reduced appetite for a week or so — normal, don't push food
- A faint pink rash as some viral illnesses resolve (roseola, viral exanthema)
- Some clinginess and unsettled sleep — recovering children often need extra contact
Send back to nursery/school when the child has been afebrile for 24 hours and is feeling well enough. UK Health Security Agency guidance says 48 hours after the last episode of vomiting or diarrhoea; 24 hours afebrile and well for most other illnesses.
When to Worry Even Without Red Flags
The most useful instrument you have is your own knowledge of your child. A parent who says "she's just not herself" — when nothing specific is wrong — is often picking up something the formal red-flag checklist would miss. Trust that instinct. If you feel something is wrong, call 111. The triage system is built to support that judgement, not override it.
Most calls reassure. Some catch genuinely serious illness early. Both outcomes are the system working as it should.
Key Takeaways
Fever is defined as a temperature above 38°C and is a normal immune response to infection — it is a symptom, not a disease. The goal of fever management in children is to make the child more comfortable, not to reach a specific temperature. In babies under three months, any fever above 38°C requires prompt medical assessment. In older children, the child's overall appearance and behaviour matter more than the exact temperature reading. Paracetamol or ibuprofen at the correct dose for the child's weight reduces fever and discomfort but does not treat the underlying cause. Fever that is persistent, high, or accompanied by specific red flag symptoms warrants medical assessment.
