A 6-year-old boy with a long-standing history of atopic dermatitis presents with severe pruritus and lichenification. On examination, the skin lesions are most prominently distributed over the flexural surfaces. Which is the most common site of involvement in childhood atopic dermatitis?

Explanation

## Most Common Sites of Atopic Dermatitis in Children **Key Point:** Flexural surfaces—antecubital fossae, popliteal fossae, neck, and wrists—are the hallmark distribution sites in childhood atopic dermatitis. ### Age-Related Distribution Pattern | Age Group | Primary Sites | Secondary Sites | |-----------|---------------|------------------| | **Infants (0–2 years)** | Face, scalp, extensor surfaces | Trunk, flexures (less common) | | **Children (2–12 years)** | Flexural surfaces (antecubital, popliteal) | Neck, wrists, ankles | | **Adolescents & Adults** | Flexures, hands, face, neck | Generalized (severe cases) | **High-Yield:** The shift from extensor (infants) to flexor (children) distribution is a classic progression in AD and is frequently tested in NEET PG. ### Why Flexural Surfaces? 1. **Increased skin moisture** — flexural areas are occluded and retain moisture, worsening barrier dysfunction 2. **Higher temperature and friction** — repeated flexion-extension trauma perpetuates inflammation 3. **Sweat accumulation** — flexures trap sweat, triggering itch-scratch cycle 4. **Reduced sebaceous gland density** — less natural lipid barrier in these areas **Clinical Pearl:** In infants, the face and extensor surfaces (cheeks, forehead, elbows, knees) are more commonly affected. As the child grows, the distribution shifts to flexural surfaces by age 2–3 years. This shift is so consistent that an adult with only extensor AD should raise suspicion for alternative diagnoses (contact dermatitis, psoriasis). **Mnemonic:** **FACE-FLEX** — Infants: **FACE** and extensor surfaces; Children: **FLEX**ural surfaces (antecubital, popliteal fossae). **Warning:** Do not confuse the distribution of childhood AD with adult AD. Infants present with facial and extensor involvement; children and adolescents present with flexural involvement. Failure to recognize this age-dependent shift can lead to diagnostic errors. [cite:Robbins 10e Ch 25]