Chapter 2 67 Follicular degeneration syndrome or central centrifugal cicatricial alopecia occurs mostly in African-American women and involves the central scalp. Folliculitis decalvans shows papular or pustular lesions and crusts on the crown. Dissecting cellulitis features boggy nodules and is associated with cystic lesions over face, axilla, groin, and buttock (Figure 16). Acne keloidalis typically affects postpubescent African-American males with papulopustular lesions along the nuchal hairline. Concluding Notes and Term Definitions Ectoderm: The ectoderm is one of the three primary germ cell layers at the early stage of the developing embryo, which is formed from the outer layer of the fertilized egg. Ectoderm has three major derivatives: surface ectoderm, neural crest, and neural tube. Ectoderm differentiates to form the nervous system (spine, peripheral nerves, Figure 15. Scarring alopecia caused by discoid lupus erythematosus Patches of complete baldness with atrophic and erythematous skin Figure 16. Scarring alopecia caused by dissecting cellulitis Boggy and balding nodules all over the scalp