Without 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:
- Fungi that can use the surface protein keratin found on the skin and especially in nails and hair, so called keratinophilic fungi
- Candida albicans that can grow on moist surfaces, such as babies bottoms if nappies cause local irritation, or in nail folds (occasionally nails themselves)
- Some non-keratinophilic filamentous fungi are able to infect damaged toenails, such as Aspergillus spp, Alternaria alternata and Fusarium spp.
Human to human transmission of keratinophilic fungi is the usual means of acquiring skin, hair and nail fungal infection, called anthropophilic infection. Occasionally animal to human transmission occurs, called zoophilic infection. Recurrent infection after treatment is likely for zoophilic infection, if contact with the animal continues and that animal is not treated. In farmers and others working outdoors, infection may be acquired from soil. The most important such fungi are Microsporum gypseum, M. fulvum and Sporothrix schenckii, all known as geophilic fungi.
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 mucocutaneous candidiasis) others acquired, including HIV infection. For example, seborrheic 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.
The common fungal infections of skin, hair and nails are: