Accordion-like structure of terminal hair follicles of the human scalp.

Terminal hair follicles extracted after ethylenediaminetetraacetic acid treatment preserved the basal cell surface of the outer root sheath well enough to examine the outer surface in detail. Light microscopic observations of whole mount specimens revealed several sawtooth-like structures of follicular epithelium in the lower portion of terminal hair follicle. Vertical sections of the human scalp also showed several invaginations of the outer root sheath of terminal hair follicles in the lower portion, not in association with the arrector pili muscle. Scanning electron microscopy of the same specimens demonstrated accordion-like structures below the sebaceous gland in the lower half of anagen terminal hair follicles and surrounding the entire circumference of the follicles. Sawtooth-like structures were unilaterally observed at the level of the middle or lower portion below the sebaceous gland. With transmission electron microscopy, these structures were seen as undulations of basal cells which preserved hemidesmosomes, although the basal lamina had been peeled off during the extraction procedure. Thus, this accordion-like structure is a genuine structural variation of some human anagen hair follicles and not an artifact.