S100A7 (psoriasin) and S100A15 (koebnerisin) were first identified in inflamed 
psoriatic skin. They are of major interest because of their putative functional 
roles in innate immunity, epidermal cell maturation, and epithelial 
tumorigenesis. Human S100A7 and S100A15 have lately evolved by gene duplications 
within the epidermal differentiation complex (chromosome 1q21) during primate 
evolution forming a novel S100 subfamily. Therefore, S100A7 and S100A15 are 
almost identical in sequence (>90%) and are difficult to discriminate. Despite 
their high homology, S100A7 and S100A15 are distinct in tissue distribution, 
regulation, and function, and thus, exemplary for the diversity within the S100 
family. Their different properties are compelling reasons to discriminate S100A7 
(psoriasin) and S100A15 (koebnerisin) in epithelial homeostasis, inflammation, 
and cancer.