Which organism is commonly responsible for onychomycosis?

• A. Candida albicans
• B. Trichophyton rubrum
• C. Aspergillus niger
• D. Microsporum canis

Answer: (B)

Onychomycosis is most often caused by dermatophytes that specialize in keratin-rich nails. The organism that most commonly drives nail infections worldwide is Trichophyton rubrum, making it the best answer. It readily invades the nail plate and nail bed, leading to the typical thickened, discolored, and sometimes detached nail seen in this condition.

Candida albicans can cause nail infections too, especially in fingernails or with chronic paronychia or immune compromise, but it is less likely to produce the classic presentation seen with dermatophyte nail infections. Aspergillus niger and Microsporum canis are much less common culprits for onychomycosis in healthy individuals, with Microsporum more often linked to skin and hair infections and Aspergillus typically seen in unusual or opportunistic settings.