**Core Concept**
Pityriasis versicolor is a common superficial fungal infection caused by Malassezia species, characterized by hypopigmented or hyperpigmented, scaly macules, often affecting the face, chest, and back.

**Why the Correct Answer is Right**
The condition is caused by the overgrowth of Malassezia species, which are naturally found on the skin surface. The fungus produces lipids that alter the skin's pigmentation, leading to the characteristic hypopigmented or hyperpigmented lesions. The presence of scaly macules and the fact that some of the boy's friends also have similar lesions suggest a contagious or infectious etiology, further supporting the diagnosis of pityriasis versicolor.

**Why Each Wrong Option is Incorrect**
**Option A:** Tinea versicolor is a more severe form of fungal infection that can cause widespread lesions, but it typically presents with a more intense inflammatory response and sometimes with a central area of clearing.
**Option B:** Pityriasis alba is a common condition in children, but it typically presents with small, round, hypopigmented patches on the face, often without scaly lesions.
**Option C:** Vitiligo is a chronic autoimmune condition characterized by the loss of pigment-producing cells, leading to well-defined areas of depigmentation, but it does not typically present with scaly lesions.

**Clinical Pearl / High-Yield Fact**
Pityriasis versicolor can be treated with topical antifungal agents, such as ketoconazole or clotrimazole, and oral antifungals, such as itraconazole or fluconazole, in more severe cases.

**Correct Answer:** D. Pityriasis versicolor.