**Core Concept**
Infantile atopic dermatitis, also known as eczema, is a chronic inflammatory skin condition characterized by dry, itchy, and scaly skin. It often presents in infants and young children, with a strong genetic predisposition.

**Why the Correct Answer is Right**
Infantile atopic dermatitis typically involves the extensor surfaces of the limbs, such as the elbows and knees. This is because these areas are more prone to dryness and irritation due to the natural environment of the skin, which is a significant factor in the pathogenesis of atopic dermatitis. The extensor surfaces are also more likely to be exposed to allergens and irritants, which can trigger an immune response and exacerbate the condition.

**Why Each Wrong Option is Incorrect**
**Option A:** Flexors, such as the antecubital fossa, are more commonly involved in adult atopic dermatitis, not infantile atopic dermatitis.
**Option C:** Head & neck involvement is more characteristic of contact dermatitis or seborrheic dermatitis.
**Option D:** Perianal area involvement is more characteristic of diaper dermatitis, a distinct entity from atopic dermatitis.

**Clinical Pearl / High-Yield Fact**
In infantile atopic dermatitis, the extensor surfaces are often more affected than the flexor surfaces, which is a key distinguishing feature from other forms of eczema.

✓ Correct Answer: B. Extensors