**Question:** Black piedra is caused by

A. Piedra black (Piedraia hortae)
B. Trichophyton
C. Aspergillus
D. Microsporum

**Correct Answer:** A. Piedra black (Piedraia hortae)

**Core Concept:** Black piedra is a fungal infection of the hair and skin caused by the fungus Piedraia hortae. It is a type of mycosis (fungal infection) that primarily affects the hair shaft and scalp, giving the appearance of a black discoloration or plug in the hair follicle.

**Why the Correct Answer is Right:** Piedraia hortae is a specific fungus responsible for causing black piedra. It is part of the Piedraia genus within the family Graphomycetaceae and is a dematiaceous (dark-colored) fungus. The infection results from direct inoculation of hair shafts, usually through traumatic injury, such as shaving or hair styling, facilitating the fungal growth and pigment production within the hair follicle.

**Why Each Wrong Option is Incorrect:**

B. Trichophyton (ringworm): Trichophyton is a group of dermatophytes involved in causing ringworm infections, which are dermatophytoses affecting the skin, hair, and nails. Black piedra is caused by Piedraia hortae, not Trichophyton.

C. Aspergillus: Aspergillus is a group of filamentous fungi responsible for causing various infections, including aspergillosis, but not black piedra.

D. Microsporum: Microsporum is another group of dermatophytes associated with ringworm infections and not responsible for black piedra.

**Clinical Pearl:** Understanding the correct causative agent of black piedra is crucial for accurate diagnosis and treatment. Black piedra should be distinguished from other fungal infections like ringworm, as the treatment approach differs.

**Explanation of the Core Concept:** Black piedra is a fungal infection caused by Piedraia hortae, which is a dematiaceous fungus. Dematiaceous fungi are characterized by melanin pigmentation in their cell walls. This infection primarily affects the hair shafts and scalp, leading to the observed black discoloration and plugging of the hair follicles. This infection is a result of direct inoculation of the fungus into the hair shafts, typically during shaving or hair styling practices.