Dermatophytes are unique in that they produce keratinase, which enables them to use keratin as a nutrient source. Infected hairs become brittle, and after three weeks, the clinical presentation of broken hairs is evident.There are three types of infection:
Ectothrix: Characterized by the growth of fungal spores (arthroconidia) on the exterior of the hair shaft. Infected hairs usually fluoresce greenish-yellow under a Wood lamp (blacklight). Associated with Microsporum canis, Microsporum gypseum, Trichophyton equinum, and Trichophyton verrucosum. Endothrix: Similar to ectothrix, but characterized by arthroconidia restricted to the hair shaft, and restricted to anthropophilic bacteria. The cuticle of the hair remains intact and clinically this type does not have fluorescence. Associated with Trichophyton tonsurans and Trichophyton violaceum, which are anthropophilic. Favus: Causes crusting on the surface of the skin, combined with hair loss. Associated with Trichophyton schoenleini. Diagnosis
Tinea capitis may be difficult to distinguish from other skin diseases that cause scaling, such as psoriasis and seborrhoeic dermatitis; the basis for the diagnosis is positive microscopic examination and microbial culture of epilated hairs. Woods lamp examination will reveal bright green to yellow-green fluorescence of hairs infected by M. canis, M. audouinii, M. rivalieri, and M. ferrugineum and a dull green or blue-white color of hairs infected by  T. schoenleinii. Individuals with M. canis infection trichoscopy will show characteristic small comma hairs. Histopathology of scalp biopsy  shows fungi sparsely distributed in the stratum corneum and hyphae extending down the hair follicle, placed on the surface of the hair shaft.
For example, Microsporum audouinii was the predominant etiological agent in North America and Europe until the 1950s, but now Trichophyton tonsurans is more common in the US, and becoming more common in Europe and the United Kingdom. This shift is thought to be due to the widespread use of griseofulvin, which is more effective against M. audounii than T. tonsurans; also, changes in immigration patterns and increases in international travel have likely spread T. tonsurans to new areas. Another fungal species that has increased in prevalence is Trichophyton violaceum, especially in urban populations of the United Kingdom and Europe. See also
List of cutaneous conditions
Ringworm affair

Footnotes
References
Richardson M. (2003). Fungal Infection: Diagnosis and Management. Cambridge, MA: Blackwell Publishers. ISBN 1-4051-1578-5. == External links ==