Differential diagnosis of the scalp hair folliculitis.

Scalp hair folliculitis is a relatively common condition in dermatological practice and a major diagnostic and therapeutic challenge due to the lack of exact guidelines. Generally, inflammatory diseases of the pilosebaceous follicle of the scalp most often manifest as folliculitis. There are numerous infective agents that may cause folliculitis, including bacteria, viruses and fungi, as well as many noninfective causes. Several noninfectious diseases may present as scalp hair folliculitis, such as folliculitis decalvans capillitii, perifolliculitis capitis abscendens et suffodiens, erosive pustular dermatitis, lichen planopilaris, eosinophilic pustular folliculitis, etc. The classification of folliculitis is both confusing and controversial. There are many different forms of folliculitis and several classifications. According to the considerable variability of histologic findings, there are three groups of folliculitis: infectious folliculitis, noninfectious folliculitis and perifolliculitis. The diagnosis of folliculitis occasionally requires histologic confirmation and cannot be based solely on clinical appearance of scalp lesions. This article summarizes prominent variants of inflammatory diseases of the scalp hair follicle with differential diagnosis and appertaining histological features.