The skin specimens were harvested at the end of the experiment, fixed with 10% formalin (Sigma-Aldrich, St. Louis, MO, USA), and embedded in paraffin for sectioning (4 μm thickness). The prepared samples were stained with hematoxylin (Sigma-Aldrich) and eosin Y (Samchun Chemical, Seoul, Korea) (H&E staining), TB staining (Sigma-Aldrich), and crystal violet (Sigma-Aldrich) and Gram’s iodine (Sigma-Aldrich) (Gram staining). The H&E-stained samples were used to measure epidermal thickness, and TB-stained samples were used to quantify the number of mast cells as previously reported (54 (link), 55 (link)). For immunohistochemical staining, the prepared sections were permeabilized with 0.2% (v/v) Triton X-100 (Wako, Osaka, Japan) and incubated with 4% (v/v) bovine serum albumin (Wako). Then, the samples were incubated with the following antibodies: mouse anti–keratin 14 (Abcam, Cambridge, CBE, UK), goat anti–MMP-9 (R&D Systems, Minneapolis, MN, USA), Alexa Fluor 488 goat anti-mouse immunoglobulin G (IgG; Thermo Fisher Scientific, Waltham, MA, USA), and Alexa Fluor 594 rabbit anti-goat IgG (Thermo Fisher Scientific). The samples were counterstained with 4′,6-diamidino-2-phenylindole (DAPI) (TCI America, Portland, OR, USA) and observed with a laser scanning confocal microscope (LSM 880; Zeiss, Jena, Germany) or a slide scanner (VS120-S5-W; Olympus, Tokyo, Japan).