In addition to filaggrin (FLG), the expression of loricrin (LOR), involucrin (IVL), and FLG2 is downregulated in the lesional and nonlesional skin of AD, resulting in an abnormal composition of the corneocyte lipid envelope surrounding corneocytes and, therefore, an impaired epidermal barrier [74]. Here, FLG is linked to Alzheimer disease.