Ectopic Sebaceous Glands in the Hair Follicle Matrix: Case Reports and Literature Review of this Embryogenic Anomaly

Hair embryogenesis is a complex process. The development of this skin appendage originates from both ectoderm and mesoderm layers. Multiple signaling pathways and regulation are required for proper hair formation. However, anomalies occasionally arise, such as ectopic sebaceous glands in the hair follicle matrix. Two men who demonstrate this developmental anomaly are reported and the characteristics of individuals in whom this aberration in hair follicle maturation has occurred are reviewed. In addition, the anatomy of the hair follicle is summarized and the embryologic features of hair morphogenesis are discussed. The occurrence of hair follicle matrix ectopic sebaceous glands is an observation of intellectual intrigue for which the pathogenesis and clinical implications remain to be determined.