**Core Concept**
Eczema herpeticum, also known as Kaposi's varicelliform eruption, is a rare and potentially life-threatening complication of atopic dermatitis (eczema) caused by a viral infection. It is characterized by a secondary bacterial or viral infection of the skin, leading to widespread skin lesions.

**Why the Correct Answer is Right**
Eczema herpeticum is primarily caused by the herpes simplex virus (HSV), type 1 or 2, which infects the skin through a break in the skin barrier in individuals with atopic dermatitis. The virus triggers an immune response, leading to inflammation and the formation of vesicles, pustules, or crusts. The lesions can become secondarily infected with bacteria, such as Staphylococcus aureus, which can exacerbate the condition.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because eczema herpeticum is not caused by a fungal infection.
**Option B:** Incorrect because while eczema herpeticum can be associated with atopic dermatitis, it is not the primary cause of eczema.
**Option C:** Incorrect because eczema herpeticum is not a type of skin cancer.

**Clinical Pearl / High-Yield Fact**
Eczema herpeticum is a medical emergency that requires prompt recognition and treatment to prevent serious complications, such as sepsis or disseminated intravascular coagulation. Early recognition and treatment with antiviral medications, such as acyclovir, can significantly improve outcomes.

**Correct Answer: D. Eczema herpeticum is a secondary infection of the skin caused by herpes simplex virus (HSV) in individuals with atopic dermatitis.**