Without a doubt, the most common human fungal infections are those affecting the skin, hair and nails. The skin is an excellent protective coat for the human body, but some fungi have a remarkable ability to survive on skin and sometimes cause infection. The fungi able to do this fall into 3 groups:
- Keratinophilic fungi that use keratin protein found on the skin, and especially in nails and hair, such as the dermatophytes
- Candida yeasts that can grow on moist skin surfaces, such as babies bottoms if nappies cause local irritation, or in nail folds (occasionally nails themselves)
- Non-keratinophilic filamentous fungi that infect damaged toenails, such as Aspergillus spp., Alternaria alternata, Fusarium spp.
Pathophysiology
TRANSMISSION: Human-to-human transmission (‘anthropophilic infection’) of keratinophilic fungi is the usual means of acquiring skin, hair and nail fungal infection, but occasionally animal-to-human transmission (‘zoophilic infection’) occurs. Recurrent infection after treatment is likely for zoophilic infection, particularly if contact with the animal continues and that animal is not treated. In farmers and others working outdoors, infection may be acquired from soil (‘geophilic infection’), most importantly Microsporum gypseum, M. fulvum and Sporothrix schenckii.
IMMUNE STATUS: The vast majority of people with fungal infection of skin, hair and nails are otherwise healthy, but a small group are immunocompromised. T-cell deficits of the immune system appear to be important, some inherited (such as CARD9 and familial mucocutaneous candidiasis) others acquired, including HIV infection. For example, seborrhoeic dermatitis and onychomycosis is often more advanced in HIV infection, and may be the first clinical sign of infection.
TREATMENT: courses tend to be long for hair and nail fungal infections because it takes time for the hair and nail to grow out, and fungi tend to persist in the keratin of the nail and hair, even in the face of antifungal therapy. CURRENT GUIDELINES
The common fungal infections of skin, hair and nails are:
