Primary scarring alopecias.

Scarring alopecia or cicatricial alopecia results from follicular damage that is sufficient to cause the destruction and replacement of pilosebaceous structures by scar tissue. Primary scarring alopecias represent a group of disorders that primarily affect the hair follicles, as opposed to secondary scarring alopecias, which affect the dermis and secondarily cause follicular destruction. Inflammation may predominantly involve lymphocytes or neutrophils. Cicatricial alopecias that mainly involve lymphocytic inflammation include discoid lupus erythematosus, lichen planopilaris, frontal fibrosing alopecia, central centrifugal alopecia, and pseudopelade (Brocq). Cicatricial alopecias that are due to predominantly neutrophilic inflammation include folliculitis decalvans, tufted folliculitis, and dissecting cellulitis of the scalp. Folliculitis keloidalis is a cicatricial alopecia with a mixed inflammatory infiltrate.