Key Facts

Atopic dermatitis is the most common inflammatory skin disease. Understanding the filaggrin-barrier defect model and the Th2 immune pathway is essential for rational treatment decisions.

Epidemiology

• UK prevalence: 15–20% of children; 2–5% of adults
• 60% develop symptoms in first year of life; 90% by age 5
• Increasing prevalence worldwide (especially in developed countries)
• Stronger maternal than paternal heritability

Aetiology

• Genetic: FLG mutations (epidermal barrier), IL-4/IL-13 pathway polymorphisms
• Environmental triggers: house dust mite, pet dander, food allergens (egg, milk — especially in young children), irritants (soap, detergents)
• Microbiome: S. aureus dominance; reduced microbial diversity
• Psychosocial: stress worsens disease

Pathophysiology

• FLG deficiency → defective cornified envelope → impaired skin barrier → increased TEWL + allergen penetration
• Th2 skewing: IL-4, IL-13 → IgE class switching, further barrier disruption
• IL-31 → itch → scratch → barrier damage → more inflammation (itch-scratch cycle)
• Chronic: Th1/Th22 involvement → lichenification

Age-Related Distribution

• Infants: face, scalp, extensor surfaces; weeping, crusting
• Children: flexures (antecubital, popliteal fossae), wrists, ankles; dry, lichenified
• Adults: hands, face, flexures; may be lichenified or nummular (discoid)

Severity Assessment

• Mild: areas of dry skin, infrequent itch
• Moderate: areas of dry skin, frequent itch, redness ± excoriations
• Severe: widespread dry skin, incessant itch, extensive redness, lichenification, bleeding, oozing

Complications

• Eczema herpeticum: widespread HSV — punched-out erosions, fever; EMERGENCY
• Secondary bacterial infection: S. aureus — crusting, pustules
• Growth restriction: in children on prolonged systemic steroids

Red Flags

• Eczema herpeticum (punched-out erosions + systemic illness)
• Erythroderma (>90% BSA)
• Failure to thrive in infant with severe eczema

Clinical Diagnosis

• Usually clinical; Hanifin & Rajka criteria

If Indicated

• Skin swab: if infected (MC&S for S. aureus; viral PCR for HSV)
• Specific IgE / skin prick tests: if food allergy suspected (children <2 with moderate-severe AD)
• Total IgE: often elevated (non-specific)
• SCORAD/EASI/POEM scores: validated severity tools for monitoring
• Patch testing: if allergic contact dermatitis component suspected
• Skin biopsy: rarely needed; shows spongiotic dermatitis

Complete Emollient Therapy

• 250–500g/week; apply frequently, especially after bathing
• Ointments (Epaderm, emulsifying ointment) for very dry skin
• Creams (Diprobase, Cetraben) for less dry/daytime use
• Soap substitute for washing

Topical Anti-Inflammatory

• Mild: hydrocortisone 1% OD-BD (face, children)
• Moderate: clobetasone butyrate 0.05%
• Potent: betamethasone valerate 0.1% (body — short courses for flares)
• Topical calcineurin inhibitors: tacrolimus 0.03%/0.1%, pimecrolimus 1% (face, flexures, long-term maintenance)
• Proactive maintenance: TCI or low-potency steroid 2×/week to previously affected areas

Adjunct Therapies

• Wet wraps: emollient ± dilute steroid under wet tubular bandages (acute flares)
• Bandages: ichthammol, zinc
• Antihistamines: sedating (hydroxyzine, chlorphenamine) at night for itch — non-sedating have no proven benefit in AD

Systemic (Specialist)

• Phototherapy: narrowband UVB
• Ciclosporin: 3–5mg/kg/day — rapid onset; monitor renal function and BP
• Methotrexate: 10–25mg weekly (slower onset than ciclosporin)
• Azathioprine: 1–3mg/kg/day (check TPMT first)
• Dupilumab: 600mg loading then 300mg SC every 2 weeks — SOLO 1&2, LIBERTY AD trials
• JAK inhibitors: baricitinib 4mg OD, upadacitinib 15–30mg OD, abrocitinib 100–200mg OD

Referral Criteria

• Dermatology: moderate-severe AD not responding to optimised topical therapy
• Urgent: eczema herpeticum, erythroderma
• Allergy: suspected food allergy (children), contact allergy (patch testing)

• 60% of childhood AD clears by adolescence
• 20% have lifelong disease (more likely with FLG mutations, early onset, severe disease)
• AD in childhood increases asthma risk by 3-fold
• QoL impact: comparable to diabetes and heart disease (DLQI studies)
• Dupilumab: sustained improvement at 52 weeks in >60% of patients

Hanifin & Rajka Diagnostic Criteria

NICE Treatment Stepladder