Key Facts

Rashes are one of the most common reasons for paediatric consultation. Most childhood rashes are caused by benign viral infections, but the ability to recognise life-threatening causes (particularly meningococcal disease) is a critical clinical skill.

Epidemiology

Virtually all children experience viral exanthems during childhood. Measles notifications in the UK have risen in recent years due to declining MMR uptake (approximately 4,000 cases in the 2023-2024 outbreak). Scarlet fever notifications have increased since 2014. Chickenpox affects ~90% of children by age 13 in unvaccinated populations. Meningococcal disease incidence is approximately 2-3 per 100,000 (reduced by MenB and MenACWY vaccination).

Aetiology

Viral exanthems: Measles, rubella, chickenpox, parvovirus B19 (fifth disease), roseola (HHV-6), hand-foot-and-mouth (Coxsackie A16), enteroviral exanthems, molluscum contagiosum

Bacterial: Scarlet fever (GAS), meningococcal disease, staphylococcal scalded skin syndrome, impetigo

Other: Kawasaki disease, Henoch-Schönlein purpura, urticaria, drug reactions, erythema multiforme

Pathophysiology

Viral exanthems result from either direct viral invasion of the skin (chickenpox) or immune-mediated response to circulating viral antigens (measles, parvovirus). The non-blanching rash of meningococcal septicaemia is caused by disseminated intravascular coagulation and capillary endothelial damage → extravasation of blood → purpura and ecchymoses. Scarlet fever rash is due to erythrogenic (pyrogenic) exotoxins produced by Group A Streptococcus.

Viral Exanthems

• Measles: Prodrome of cough, coryza, conjunctivitis, Koplik spots (white spots on buccal mucosa); maculopapular rash day 3-5 spreading from behind ears/hairline → face → trunk → limbs; high fever
• Rubella: Mild illness; pink macular rash face → trunk (fades in 3 days); suboccipital/postauricular lymphadenopathy; teratogenic
• Chickenpox: Crops of vesicles (macule → papule → vesicle → pustule → crust); different stages simultaneously; centripetal; pruritic
• Parvovirus B19 (fifth disease): 'Slapped cheek' facial erythema then reticular/lace-like rash on limbs; arthralgla in adults
• Roseola (HHV-6): High fever for 3-5 days then diffuse macular rash as fever breaks; age 6 months-2 years; febrile seizures common
• Hand, foot and mouth: Vesicles on palms, soles, and oral mucosa; mild fever; self-limiting

Bacterial

• Scarlet fever: Sore throat → sandpaper-like erythematous rash (spares face except flushed cheeks with circumoral pallor); strawberry tongue; Pastia lines (linear petechiae in skin folds)
• Meningococcal septicaemia: Non-blanching petechiae/purpura, rapidly evolving; fever, tachycardia, poor perfusion, altered consciousness
• Impetigo: Honey-crusted lesions (non-bullous) or large flaccid blisters (bullous); face/perioral common

Other Important Rashes

• Kawasaki disease: Fever ≥5 days + ≥4 of: bilateral conjunctivitis, oral changes, rash, extremity changes, cervical lymphadenopathy
• HSP: Palpable purpura (buttocks/legs), arthralgia, abdominal pain, haematuria
• Erythema multiforme: Target lesions; can be triggered by HSV, mycoplasma

Red Flags

• Non-blanching rash + unwell child → meningococcal disease: give benzylpenicillin and call 999
• Fever ≥5 days → consider Kawasaki disease
• Vesicular rash in immunocompromised → severe varicella risk
• Rash with airway compromise → anaphylaxis or epiglottitis
• Rash in neonate → neonatal HSV (high mortality without treatment)

Bedside

• Full skin examination: Distribution, morphology (macules, papules, vesicles, pustules, petechiae/purpura), blanching
• Glass/tumbler test: Non-blanching → meningococcal disease must be excluded
• Observations: Temperature, HR, RR, BP, CRT, SpO2
• Throat examination: Tonsillitis, Koplik spots, strawberry tongue
• Urine dipstick: Haematuria/proteinuria in HSP

Bloods

• FBC, CRP: If systemically unwell; if meningococcal disease suspected
• Blood cultures: If septicaemia suspected
• Meningococcal PCR: Blood — if meningococcal disease suspected
• Serology: Measles IgM, parvovirus IgM, rubella IgM — specific viral diagnosis
• ASO titre: If post-streptococcal complication suspected
• Echocardiography: If Kawasaki disease suspected (coronary artery aneurysms)

Imaging

• CXR: If respiratory complications (measles pneumonia, varicella pneumonia)
• Echocardiography: Kawasaki disease — baseline and at 6 weeks

Special Tests

• Oral fluid swab: For measles IgM (salivary — notifiable disease investigation)
• Vesicle fluid PCR: Varicella/HSV if diagnostic uncertainty
• Skin biopsy: Rarely needed; consider if vasculitis or atypical presentation
• Lumbar puncture: If meningitis suspected (defer if shocked — treat empirically)

Non-pharmacological

• Most viral exanthems: Supportive care — rest, fluids, antipyretics for comfort
• Chickenpox: Keep child away from school until all vesicles have crusted (usually 5-7 days); avoid aspirin (Reye syndrome risk)
• Measles: Notifiable disease — inform PHE; supportive care; consider vitamin A in severe cases
• Infection control: Isolation for measles, chickenpox; hand hygiene for HFMD; 48-hour exclusion for impetigo after starting treatment

Pharmacological

• Scarlet fever: Phenoxymethylpenicillin 12.5mg/kg QDS for 10 days (first-line); azithromycin if penicillin-allergic
• Meningococcal disease:
  • Pre-hospital: IM benzylpenicillin (300mg <1 year, 600mg 1-9 years, 1.2g ≥10 years)
  • Hospital: IV ceftriaxone 80mg/kg (max 4g) OD; fluid resuscitation; PICU if shocked
• Chickenpox in immunocompromised: IV aciclovir 10mg/kg TDS for 7-10 days; oral aciclovir 20mg/kg QDS (max 800mg) for high-risk contacts within 24h of rash
• Impetigo: Topical fusidic acid 2% TDS for 5 days (localised); oral flucloxacillin 12.5-25mg/kg QDS for 7 days (widespread)
• Kawasaki disease: IV immunoglobulin 2g/kg single infusion + aspirin 30-50mg/kg/day (high dose) then 3-5mg/kg/day for 6-8 weeks
• HSP: Supportive; analgesia; corticosteroids for severe abdominal pain or nephritis (specialist decision)

Surgical/Interventional

• Not applicable for most childhood rashes

Referral Criteria

• Non-blanching rash + unwell — emergency admission
• Suspected Kawasaki disease — urgent paediatric assessment
• Measles — notifiable; PHE notification
• Scarlet fever — notifiable; PHE notification
• Immunocompromised child with chickenpox — immediate specialist assessment

• Most viral exanthems: Self-limiting, full recovery within 1-2 weeks
• Measles: Complications in ~30% (otitis media, pneumonia, encephalitis ~1:1,000, SSPE ~1:25,000); mortality ~1-2 per 1,000 in developed countries
• Chickenpox: Usually mild; severe in neonates, immunocompromised, adults; mortality 1-2 per 100,000 children
• Scarlet fever: Excellent prognosis with antibiotics; rare complications include rheumatic fever, post-streptococcal GN
• Meningococcal disease: Mortality ~5-10% even with treatment; ~25% of survivors have long-term sequelae (hearing loss, limb loss, cognitive impairment)
• Kawasaki disease: Coronary artery aneurysms in ~25% untreated; <5% with timely IVIg treatment
• HSP: Self-limiting in most; ~5% develop significant renal disease

Classic Childhood Exanthems

Notifiable Diseases (Rash-Related)