**Core Concept**
Nikolsky sign is a clinical indicator used to assess the integrity of the skin or mucous membrane. It is a positive sign when gentle pressure or rubbing results in the exfoliation or separation of the outer layer of the skin or mucosa from the underlying layer.

**Why the Correct Answer is Right**
Bullous pemphigoid is a chronic autoimmune skin disease characterized by the formation of blisters on the skin. The disease is caused by the presence of autoantibodies against the basement membrane zone of the skin. However, the blisters in bullous pemphigoid are not fragile and do not exhibit the characteristic slippage of the epidermis over the dermis when subjected to pressure or rubbing, which is the hallmark of a positive Nikolsky sign. In contrast, conditions like pemphigus, toxic epidermal necrolysis, and staphylococcal scalded syndrome exhibit a positive Nikolsky sign due to the disruption of intercellular connections in pemphigus, the separation of the epidermis from the dermis in toxic epidermal necrolysis, and the exfoliative toxin-mediated separation of the epidermis in staphylococcal scalded syndrome.

**Why Each Wrong Option is Incorrect**
**Option A:** Pemphigus is characterized by the disruption of intercellular connections between keratinocytes, resulting in a positive Nikolsky sign.
**Option C:** Toxic epidermal necrolysis is a severe skin condition caused by the separation of the epidermis from the dermis, resulting in a positive Nikolsky sign.
**Option D:** Staphylococcal scalded syndrome is caused by the exfoliative toxin of Staphylococcus aureus, which separates the epidermis from the dermis, resulting in a positive Nikolsky sign.

**Clinical Pearl / High-Yield Fact**
It is essential to remember that a positive Nikolsky sign is indicative of diseases that affect the integrity of the skin or mucous membrane, such as pemphigus, toxic epidermal necrolysis, and staphylococcal scalded syndrome. In contrast, conditions like bullous pemphigoid do not exhibit a positive Nikolsky sign due to the presence of autoantibodies against the basement membrane zone of the skin.

**✓ Correct Answer: B. Bullous pemphigoid**