Candida Onychomycosis Candida Onychomycosis in a 26 year old male - Onychomycosis is a fungal infection of the fingernails or toenails that results in thickening, roughness, and splitting of the nails. It is usually caused by Trichophyton rubrum or T. mentagrophytes; in this case caused by candida. Also called tinea unguium