The clinical and mycologic features and pathogenesis of onychomycosis show that there are four clinical types distinguished by apparently unique host-parasite relationships in which the pathogenic fungus, either alone or in combination with associated microbial flora, acts in a characteristic biochemical manner to produce nail destruction. The four clinical types are distal subungual onychomycosis, white superficial onychomycosis, proximal subungual onychomycosis and Candida onychomycosis.
Zaias N. Onychomycosis. Arch Dermatol. 1972;105(2):263-274. doi:10.1001/archderm.1972.01620050069017