**Core Concept**
Pityriasis rosea is a skin condition characterized by the appearance of a herald patch followed by a secondary eruption of oval-shaped, scaly plaques. The pathophysiology of pityriasis rosea involves an immune-mediated reaction to a viral infection, likely human herpesvirus 6 (HHV-6) or human herpesvirus 7 (HHV-7).

**Why the Correct Answer is Right**
The characteristic skin lesions in pityriasis rosea are typically 2-10 cm in diameter and have a fine collarette of scale at the periphery. The lesions often have a distinctive "Christmas tree" distribution on the trunk and proximal extremities. This distribution is due to the predilection of the lesions to appear on the skin areas that are exposed to the sun.

**Why Each Wrong Option is Incorrect**
**Option A:** The herald patch is a characteristic feature of pityriasis rosea, and it is often the first sign of the disease. Therefore, it is a characteristic of pityriasis rosea.

**Option B:** The skin lesions in pityriasis rosea are typically oval-shaped and have a fine collarette of scale at the periphery. This is a characteristic feature of the disease.

**Option C:** Pityriasis rosea often presents with a "Christmas tree" distribution on the trunk and proximal extremities. This is a characteristic feature of the disease.

**Clinical Pearl / High-Yield Fact**
The "Christmas tree" distribution of pityriasis rosea is a classic dermatological finding that should be remembered by students. This distribution is due to the predilection of the lesions to appear on the skin areas that are exposed to the sun.

**Correct Answer:** D