Results The transcriptome of the aging human epidermis Primary human epidermis samples were obtained as suction blisters from the inner forearm of five female donors from two distinct age groups (18–24 years and 70–75 years, see Additional file 1: Table S1 for details), respectively. These two age groups provide a good representation of the skin aging phenotype in healthy adults [17]. After RNA purification, samples were pooled in equimolar ratios to allow library preparation for transcriptome sequencing. Pooling of samples was required to obtain sufficient amounts of mRNA for library prep- aration. Paired-end sequencing on an Illumina HiSeq 2000 platform with read-lengths of 105 bases generated 90 Gb of DNA sequence. After trimming to a maximal read length of 80 bases and a minimum base quality of a 30 Phred score, sequence reads were mapped to the GRCh37/hg19 reference sequence using TopHat [19]. The resulting average strand-specific genome coverages were 500x for each sample