Medical Encyclopaedia › Nail fungus (short definition)
In brief: Nail fungus (onychomycosis) is a fungal infection of the fingernails or, more often, the toenails. The nails become discoloured, thick and brittle. Without treatment, nail fungus hardly ever heals by itself.
Signs
The infection usually begins at the front edge of the nail with whitish-yellowish discoloration that slowly spreads towards the nail bed. Later the nail thickens, crumbles and can detach. Athlete’s foot is often present at the same time.
Transmission and risk factors
The pathogens, usually dermatophytes, are transmitted in warm, humid environments such as swimming pools, saunas and changing rooms. Circulatory disorders, diabetes, a weakened immune system, tight footwear and athlete’s foot are contributing factors.
Treatment
Before treatment, the fungus should ideally be confirmed by a sample, as other nail diseases can look similar. If only part of the nail is affected, medicated nail lacquers containing ciclopirox or amorolfine, applied over many months, are often sufficient. In the case of extensive infection or several nails, tablets such as terbinafine are used in addition. As a nail grows back slowly, treatment often takes six to twelve months.
Prevention
Drying the feet thoroughly, including between the toes, wearing pool shoes in communal showers, washing socks at at least 60 °C and treating athlete’s foot early reduce the risk of nail fungus and relapses.
Related terms in the encyclopaedia
Athlete’s foot, Antifungal, Terbinafine, Candida, Diabetic foot
Sources
- Deutsche Dermatologische Gesellschaft (DDG): S1-Leitlinie Onychomykose
- IQWiG: gesundheitsinformation.de – Gesundheitsinformationen des Instituts für Qualität und Wirtschaftlichkeit im Gesundheitswesen
Note: This article is for general information and does not replace advice, diagnosis or treatment from a doctor or pharmacist. Last updated: October 2026.