(favus) A severe, chronic fungal skin infection, usually of the scalp, characterized by the development of thick, yellow cup-shaped crusts and scarring over hair follicles.

A disease of the scalp that may affect the glabrous skin and the nails and is recognized by the concave sulfur-yellow crusts that form around loose, wiry hairs. Atrophy ensues, leaving a smooth, glossy, thin, paper-white patch. This type of disease is rare in the United States and more frequently seen in the Middle East, Africa, Southeastern Europe, and other countries bordering the Mediterranean Sea. (Arnold, Odom, and James, Andrew's Diseases of the Skin, 8th ed, p319)

Favus, also termed tinea favosa, is a chronic inflammatory dermatophytic infection usually caused by Trichophyton schoenleinii. Rarely, favus is caused by Trichophyton violaceum, Trichophyton mentagrophytes var quinckeanum, or Microsporum gypseum.