Which organism causes ringworm of the scalp?

• A. Bacteria
• B. Protozoa
• C. Virus
• D. Dermatophyte fungus

Answer: (D)

Ringworm of the scalp is a fungal infection that directly invades keratin in skin and hair. The organisms responsible are dermatophyte fungi, a group that includes species like Trichophyton and Microsporum. These fungi produce keratinase, allowing them to digest keratin and spread through the scalp hair and skin, which is why the infection presents as scaly patches with possible hair breakage.

This differentiates it from the other options: bacteria cause bacterial skin infections, viruses cause viral infections, and protozoa cause different parasitic infections. The term ringworm reflects the outward circular expansion of the lesion as the fungus grows, leading to the characteristic ring-like appearance seen with tinea capitis.