Onychomycosis is a topic covered in the 5-Minute Clinical Consult.

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  • Fungal infection of fingernails/toenails
  • Caused mostly by dermatophytes but also yeasts and nondermatophyte molds
  • Toenails are more commonly affected than fingernails.
  • System(s) affected: skin, exocrine
  • Synonym(s): tinea unguium; ringworm of the nail


  • Occurs in 2–10% of general population
  • Predominant age: 20% in adults >60 years of age
  • Rare before puberty
  • Prevalence 15–40% in persons with human immunodeficiency infection (1)

Etiology and Pathophysiology

  • Dermatophytes: Trichophyton (Trichophyton rubrum most common), Epidermophyton, Microsporum
  • Yeasts: Candida albicans (most common), Candida parapsilosis, Candida tropicalis, Candida krusei
  • Molds: Scopulariopsis brevicaulis, Hendersonula toruloidea, Aspergillus sp., Alternaria tenuis, Cephalosporium, Scytalidium hyalinum
  • Dermatophytes cause 90% of toenail and most of fingernail onychomycoses.
  • Fingernail onychomycosis is more often caused by yeasts, especially Candida.
  • Dermatophytes can invade normal keratin, whereas nondermatophyte molds invade altered keratin (dystrophic/injured nails).

Risk Factors

  • Older age
  • Tinea pedis
  • Occlusive footwear
  • Cancer/diabetes/psoriasis
  • Peripheral vascular disease
  • Cohabitation with others with onychomycosis
  • Immunodeficiency
  • Communal swimming pools
  • Smoking
  • Peripheral vascular disease
  • History of nail trauma
  • Autosomal dominant genetic predisposition

Commonly Associated Conditions

  • Immunodeficiency/chronic metabolic disease (e.g., diabetes)
  • Tinea pedis/manuum

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