Child Fever — Causes, Symptoms, When to Worry & Treatment Guide — Symptoms, Causes & Treatment | MyMedicPlus

Fever in children is defined as a body temperature above 38°C (100.4°F), measured rectally (most accurate), tympanically (ear), axillary (armpit — 0.5°C below true core temperature), or orally. It is the most common presenting symptom in paediatric medicine, accounting for 20-30% of all paediatric emergency visits. Fever itself is a physiological immune response — not a disease — that helps fight infection by creating an unfavourable environment for pathogens and enhancing immune function. The height of the fever does not reliably predict the severity of the underlying illness, particularly in young infants. What matters most in assessing a febrile child is their behaviour, hydration status, and clinical appearance rather than the exact temperature. Viral infections account for the vast majority of childhood fevers.

The most common cause of fever in children is viral infection — upper respiratory tract infections (common cold, influenza, pharyngitis, croup, bronchiolitis caused by RSV), gastrointestinal viruses (rotavirus, norovirus), and viral exanthems (roseola infantum — HHV-6, causing high fever then rash in children under 2; chickenpox; measles). Bacterial causes that must not be missed: urinary tract infection (UTI — most common serious bacterial infection in children under 5; fever may be the only sign), pneumonia, septicaemia, meningitis, and otitis media. Other causes: post-immunisation fever (common 12-24 hours after DTaP, MMR, meningococcal vaccines — self-limiting), teething (low-grade fever only, above 38°C is NOT caused by teething alone — always investigate), and rarer inflammatory conditions (Kawasaki disease — prolonged fever above 5 days with rash, mucositis, lymphadenopathy, conjunctivitis).

In most febrile children, symptoms are those of the underlying infection. The child may appear unwell, irritable, or flushed with hot skin. They may refuse feeds (infants) or food (older children), sleep more than usual, and have associated symptoms depending on the cause: runny nose and cough (URTI), vomiting and diarrhoea (gastroenteritis), ear pain (otitis media), sore throat (pharyngitis), or rash. Red flag signs requiring emergency assessment: age under 3 months with any fever; age 3-6 months with temperature above 39°C; non-blanching rash (petechiae or purpura — possible meningococcal disease — medical emergency); bulging fontanelle (meningitis); stiff neck; photophobia; seizure; extreme pallor or mottled skin; inconsolable crying; high-pitched or unusual cry in infants; difficulty breathing; reduced consciousness; and signs of severe dehydration (sunken eyes, dry mouth, no urine for 8+ hours).

Clinical assessment is the cornerstone, using the NICE traffic light system: green (low risk — mild illness, normal colour, responding to social cues); amber (intermediate risk — pallor, decreased activity, prolonged capillary refill — requires investigations and urgent review); red (high risk — pale/mottled/ashen skin, non-responsive, ill-appearing — requires immediate emergency care). Investigations depend on clinical assessment: urine dipstick and MSSU culture (UTI in all children under 3 years, or any age with unexplained fever above 38°C lasting more than 48 hours); blood tests (FBC, CRP, blood cultures, procalcitonin — for suspected serious bacterial infection); chest X-ray (suspected pneumonia); lumbar puncture (if meningitis suspected). NICE recommends measuring temperature with electronic/chemical-dot thermometer (rectal route most accurate in infants under 4 weeks).

Antipyretics reduce discomfort but do not shorten the illness course or prevent febrile convulsions. Use when the child is distressed or uncomfortable. Paracetamol (acetaminophen): 15 mg/kg every 4-6 hours (maximum 4 doses in 24 hours; maximum 1g per dose in older children/adolescents) — safe from birth. Ibuprofen: 5-10 mg/kg every 6-8 hours (maximum 3 doses in 24 hours) — use in children over 3 months and over 5 kg; avoid in dehydrated children, suspected chickenpox, and renal impairment. Alternating paracetamol and ibuprofen every 2-3 hours is sometimes used for persistent high fever causing significant distress (NICE accepts this approach though evidence is limited). Never give aspirin to children under 16 (Reye's syndrome risk). Maintain adequate fluid intake — offer frequent small amounts. Tepid sponging, fans, and cold baths are not recommended (worsen shivering and discomfort). Treat the underlying cause: antibiotics for confirmed bacterial infections (UTI, pneumonia, sepsis); antiviral medications (oseltamivir/Tamiflu for influenza in high-risk groups).

Most viral childhood fevers resolve without complications. The greatest risk from inadequate assessment is missing serious bacterial infection — meningococcal disease (Neisseria meningitidis) carries 10% mortality even with optimal treatment, and 15-20% of survivors suffer permanent disabilities including limb amputation, deafness, brain damage, and disfiguring skin scarring. Meningococcal septicaemia can progress from mild fever to circulatory collapse within hours. Febrile seizures (convulsions triggered by rapid fever rise) affect 2-5% of children — most simple febrile seizures are benign, but prolonged febrile seizures (status febrilis, lasting more than 30 minutes) cause hypoxic-ischaemic brain injury. Untreated urinary tract infection in young febrile children causes renal cortical scarring, hypertension, and chronic kidney disease — particularly with high-grade vesicoureteric reflux.

Vaccination is the most effective prevention — the UK childhood immunisation schedule protects against many causes of childhood fever including meningococcal disease, pneumococcal infection, Hib, whooping cough, measles, mumps, rubella, and influenza. Annual influenza vaccination is recommended for all children aged 2-18 years in the UK (nasal spray live attenuated vaccine). Good hand hygiene — handwashing with soap and water for 20 seconds — significantly reduces transmission of viral and bacterial infections. Breastfeeding reduces the incidence and severity of respiratory and gastrointestinal infections in infants. Keep children home from school or nursery until fever-free for 24 hours without antipyretics.

Call 999/emergency services or go immediately to A&E for: a non-blanching rash (does not fade when pressed with a glass — possible meningococcal disease); seizure; baby under 3 months with any fever; rapid deterioration in condition; difficulty breathing or cyanosis (blue lips); a child who is unresponsive or cannot be woken; and extreme pallor or mottled skin. Contact your GP or call 111 (UK) same day for: any baby aged 3-6 months with fever above 38°C; any child with fever above 39°C lasting more than 48 hours; a febrile child who appears increasingly unwell, is not improving, or whose parent is concerned. Trust parental instinct — a parent's sense that 'something is wrong' should always be taken seriously.