The reduced mRNA expression of ELOVL1 and ELOVL4 in FAg-induced AD-like dermatitis in the present study and the reduced protein expression of ELOVL1 in the SC of human AD patients shown by Danso et al. [44] suggest that the carbon chain length of free FAs in the SC may also be regulated by a common synthetic pathway, and free FAs may also play important roles in the skin barrier function. Here, ELOVL4 is linked to Alzheimer disease.