**Core Concept**
The presentation of oval scaly hypopigmented macules on the chest and back is suggestive of a condition characterized by abnormal cell-mediated immunity, leading to impaired skin barrier function and susceptibility to fungal infections.

**Why the Correct Answer is Right**
The correct answer is **Pityriasis Versicolor**, a superficial fungal infection caused by Malassezia species. This condition is more common in individuals with oily skin, particularly in the chest and back areas. The oval scaly hypopigmented macules are characteristic of Pityriasis Versicolor, which results from the impaired skin barrier function and the presence of Malassezia species that feed on sebum, leading to the formation of scaly lesions.

**Why Each Wrong Option is Incorrect**
**Option A:** **Psoriasis** is a chronic autoimmune condition characterized by well-defined erythematous scaly plaques, not typically hypopigmented.

**Option B:** **Vitiligo** is a condition characterized by well-defined depigmented macules, not necessarily scaly.

**Option C:** **Pityriasis Alba** is a condition characterized by faint, scaly hypopigmented patches, primarily seen in children, and not typically on the chest and back.

**Clinical Pearl / High-Yield Fact**
Pityriasis Versicolor is more common in individuals with oily skin, and the lesions often fade or change color with sun exposure, making it essential to consider this condition in the differential diagnosis of scaly hypopigmented macules on the chest and back.

**Correct Answer:** D. Pityriasis Versicolor