(A) S. epidermidis and (B) P. acnes added to the medium of reconstructed human epidermal equivalents induce dose-dependent changes in the expression of genes involved in differentiation (FLG, TG1, CLD, OCCL) and proliferation (PCNA). After 24 hrs incubation with bacteria at 1 × 107, 1 × 108 and 1 × 109 CFU, RNA from the RHEs was extracted and reverse transcribed. The mRNA expression levels of a range of genes were determined by quantitative reverse transcription polymerase chain reaction. The amount of target transcripts was normalized using an 18S RNA normalization gene. Data are expressed as percentage of untreated control (UnC = 100%) and are presented as mean ± one standard deviation. Asterisks indicate statistically significant differences (P < 0.05) vs the untreated control.