In their article, Piraccini and Tosti better define the deep variant of white superficial onychomycosis (WSO). The authors observe deep WSO in 3 situations: (1) mold infections (particularly Fusarium species and Aspergillus species infections), (2) children with Candida or Trichophyton rubrum infection, and (3) immunocompromised patients with T rubrum infection. Deep WSO is characterized by diffuse involvement of the nail plate and presence of fungi in both the superficial and intermediate layers. Traditionally, the toenails are affected; however, in children and immunocompromised patients, deep WSO can also affect fingernails. Certain host factors may affect the severity of WSO including immune function, genetics, and local factors such as nail thickness.