Global and local graphing of the test results is a necessary step for interpreting genome-wide association studies. A widely used graphical viewing method is the Manhattan plot, which helps to quickly identify genome locations in a chromosome [23]. There-fore, a genome-wide transcriptional profiling analysis and Manhattan plotting were used to examine the mechanism of irritation of RA and HQ, which suggested that chromosome 1q21 was one of the loci associated with DEGs (Fig. 1). The expression pattern of DEG cluster in chromosome 1q21 in response to RA treatment was generally inverse to that by HQ and SLS (Fig. 1). In addition, the validation to evaluate expression of genes encoding structural proteins in chromosome 1q21 using subcytotoxic doses of RA, HQ, and SLS control, which were used for microarray analysis to minimize changes in gene expression due to cell death [24], identified the transcriptional profile results (Fig. 2 and Table S1A and B). Loricrin expression, although reportedly too low to be detectable in monolayered cultures [25], was examined at the mRNA level. RA decreased Loricrin mRNA, while HQ or SLS treatment caused an increase (Fig. 2). In chromosomal region 1q21, there is a cluster of genes encoding the cornified envelope precursors, such as loricrin, involucrin and small proline-rich proteins (SPRRs); intermediate filament-associated proteins, such as profilaggrin and trichohyalin; and several S100A calcium-binding proteins [18–21]. The cornified envelope con- stitutes the principal barrier to percutaneous penetration of exogenous substances. Therefore, these results suggested that effect of RA on the modulation of structural genes of the physiological skin barrier may be different from that of HQ or SLS (Fig. 2). Irritant potential in vitro is correlated with reduced cell viability and increased cytotoxicity. Because concentrations that inhibit cell viability by 50% have been used as threshold concentrations of irritation on human skin [14], subcytotoxic doses may not be sufficient to identify the irritation mechanism. Concentration-dependent effects on cornified envelope-associated proteins expression, including TG-1 showed that RA reduced the expression levels of filaggrin, SPRR1A/1B, and TG-1 at the concentrations producing