Hair casts: classification, staining characteristics, and differential diagnosis.

Considerable confusion exists in the literature regarding hair casts. A variety of different disorders have been grouped and reported as if they were a single entity. This nonspecificity in terminology accounts for the vast discrepancy in their reported incidence, size, configuration, etc. A specific classification for hair casts is proposed to clarify the situation. This article presents a practical staining technic, which readily differentiates peripilar keratin casts from other hair disorders. Clinical and microscopic characteristics of peripilar keratin casts and peripilar nonkeratin casts are illustrated.