What is the difference between onychomycosis and tinea unguium? What organisms most commonly cause tinea unguium? Where does the infection typically start?

Whereas onychomycosis includes all fungal infections of the nail (dermatophytes and others), tinea unguium refers specifically to dermatophyte infection of the nail. The most common organisms are Trichophyton rubrum (most common), T. mentagrophytes, and Epidermophyton floccosum. The vast majority of infections start at the distal end of the nail. Proximal subungual infections are quite rare in people with normal immune systems.