Recent studies have demonstrated TSLP, as an autocrine and paracrine factor, produced mainly by mutant bulge hair follicle stem cells and basal keratinocytes, can stimulate adjacent non-mutant epidermal cells to hyper-proliferate and express vascular endothelial growth factor α, thus contributing to skin inflammation and epidermal hyperplasia in PVs patients (74). This evidence concerns the gene TSLP and perivascular space measurement.