It has been hypothesized that milia originate from the hair bulge of the outer root sheath. To elucidate the histogenesis of milia, an immunohistochemical study was performed using anti‑keratin and anti‑filaggrin antibodies to determine the levels of keratin and filaggrin expression. Keratin expression was evaluated using anti‑keratin antibodies against K1, K7, K8, K10, K14, K15, K16, K17, K18, K19 and K20. K1 and K10 expression were detected in the suprabasal layers of the more superficial section of the cyst walls, but not in the deeper section of the cyst walls. However, K14 and K17 were expressed in all layers of the cyst walls. Notably, K15 was expressed in the outermost layer of the deeper section of the cyst walls and hair germ structure, whereas filaggrin was expressed in the superficial layer of the more superficial section of the cyst walls. Therefore, the pattern of keratin and filaggrin expression indicates that milia may originate from the outermost cells of the hair bulge of the outer root sheath.

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