Onchomycosis: an overview.

Onychomycosis is a fungal infection of the nail unit, more common in toenails than in fingernails, and caused by a variety of fungi including dermatophytes, nondermatophyte molds, and <em>Candida.</em> There are 4 to 5 subtypes related to the method of fungal invasion of the nail unit, the most common being distal lateral subungual onychomycosis. Here the fungus enters the distal lateral part of the nail bed, the region of the hyponychium, often as an extension of tinea pedis. Hyperkeratosis occurs under the nail plate, resulting in detachment of the nail plate from the nail bed (onycholysis), with subungual thickening.