Moreover, a low serum vascular endothelial growth factor (VEGF) level has been found to predict AD persistence in infancy [73], while the enzyme indoleamine 2,3-dioxygenase-1 (IDO1) has been proposed as a prognostic candidate biomarker for the development of eczema herpeticum and other viral complications in AD patients [74]. Here, IDO1 is linked to herpes simplex dermatitis.