Deletion of Cers4 leads to inflammatory alterations resembling human AD. (A) FACS analysis of CD45, CD4⁺, Th2, ILC2, ILC1, ILC3, Th17, and natural killer (NK) cells in control (Ctr) and CerS4^epi−/− ears (Ctr = 10, CerS4^epi−/− = 12 mice/genotype, mean ± SD; unpaired t test). (B) GSEA of transcriptional profiles from patients diagnosed with AD (Federico et al., 2020) in differentially expressed genes in Ctr and CerS4^epi−/− skin. NES, normalized enrichment score. (C) Annotation enrichment analysis of in human phenotype ontology terms in differentially expressed proteins in Ctr and CerS4^epi−/− organoids. (D) Model of how CerS4 deletion in HFSCs leads to hair loss and eczema.