Various disorders affect pilosebaceous units, although these diseases are rarely life threatening. Three types of skin cysts exist: epidermoid cysts result from squamous metaplasia of a damaged sebaceous gland, while trichilemmal cysts and steatocys-toma are both genetically determined structural aberrations of the pilosebaceous duct. Accumulation of material in the follicular lumen results in distension of the follicle, leading to the formation of noninflamed lesions that are typical of acne, which is the most common follicular disease. In terminal follicles, plugging of the pilosebaceous duct may occur and result in keratosis pilaris. Inflammation around follicles is often seen at the skin surface, for example in folliculitis or acne. In folliculitis, there is extensive colonization of the follicular lumen by microflora.
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