Onychomycosis (cont.)

Medical Author:

John Ratz, MD, MBA

Coauthor:

Jessica B Johnson

Medical Editor:

Dirk M Elston, MD

Medical Editor:

Mary L Windle, PharmD

Medical Editor:

Ronald A Greenfield, MD

Causes of Onychomycosis

Onychomycosis is caused by 3 main classes of organisms: dermatophytes (fungi that infect hair, skin, and nails and feed on nail tissue), yeasts, and nondermatophyte molds. All 3 classes cause the same symptoms, so the appearance of the infection does not reveal which class is responsible for the infection. Dermatophytes (including Epidermophyton, Microsporum, and Trichophyton species) are, by far, the most common causes of onychomycosis worldwide. Yeasts cause 8% of cases, and nondermatophyte molds cause 2% of onychomycosis cases.

• The dermatophyte Trichophyton rubrum is the most common fungus causing distal lateral subungual onychomycosis (DLSO) and proximal subungual onychomycosis (PSO).

• The dermatophyte Trichophyton mentagrophytes commonly causes white superficial onychomycosis (WSO), and more rarely, WSO can be caused by species of nondermatophyte molds.

• The yeast Candida albicans is the most common cause of chronic mucocutaneous candidiasis (disease of mucous membrane and regular skin) of the nail.

Risk factors for onychomycosis include family history, advancing age, poor health, trauma, living in a warm climate, participation in fitness activities, immunosuppression (can occur from HIV or certain drugs), bathing in communal showers (such as at a gym), and wearing shoes that cover the toes completely and don’t let in any airflow.