Neoscytalidium dimidiatum and Scytalidium hyalinum are molds belonging to the genus Scytalidium that may cause superficial fungal infections including onychomycosis.

They are found in soil, plants, and fruit trees, particularly in tropical and subtropical countries, but may be found throughout the world.

These organisms invade the plantar feet, webs, and toenails and less commonly affect the hands. Since these molds are associated with soil, there is usually a history of the patient walking barefoot. Distal lateral subungual onychomycosis is the most common subtype, but total dystrophic onychomycosis may ensue with long-standing infections. Onycholysis, subungual hyperkeratosis, and brown-black pigmentation are common. Paronychia may also occur.

Diagnosis is made by microscopic examination followed by fungal culture using cycloheximide-free media. Polymerase chain reaction (PCR) may also be used. Clinical judgement is necessary to determine if a positive culture is indicative of infection or contamination (as Scytalidium species are a frequent environmental contaminant).

Treatment of this infection is very difficult, as there are no standard therapies and resistance is common.