Which organism is commonly responsible for onychomycosis?

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

Answer: (B)

Trichophyton rubrum is the organism most commonly responsible for onychomycosis because it is a dermatophyte that specializes in keratin-rich tissues like nails. It produces keratin-degrading enzymes and spreads readily within the nail unit, making it the frequent cause of nail infections worldwide, especially distal and lateral subungual types. While Candida albicans can infect nails too, particularly the fingernails, it’s less common overall. Aspergillus niger and Microsporum canis can cause nail infections but are far less typical culprits than dermatophytes, and Microsporum canis is more often linked to animal exposures. So the best-supported, most common cause is Trichophyton rubrum.