IL13 and Alzheimer disease: Importantly, Zhang and co-authors [184] linked the cytokine milieu of AD to sebocyte function by showing that IL-4 and IL-13 upregulate the expression of 3β-hydroxysteroid dehydrogenase 1 (3β-HSD1), a key rate-limiting enzyme in the biosynthesis of sex steroid hormones from adrenal precursors, which is predominantly expressed by SGs in human skin [185].