Transdermal sensitization by Glupearl 19S, which is a hydrolyzed wheat protein with a molecular weight of tens of thousands and present in a facial soap, has been reported. Intact skin is considered to function as a barrier; thus, a substance with molecular weight as high as that of Glupearl 19S cannot penetrate to the skin and cause sensitization. We studied whether moderate- or high-molecular-weight materials could penetrate into the skin by using intact and injured Yucatan micropig skin in vitro. Fluorescein isothiocyanate (FITC)-labeled dextran (MW 4000, FD4) and ovalbumin (FITC-OVA) were applied as 1% aqueous solutions with or without 1% sodium dodecyl sulfate (SDS) as a surfactant. FD4 penetrated in the stratum corneum of intact and delipidized skin, especially when combined with SDS. It also penetrated into the dermis of stripped skin (the stratum corneum was removed by tape stripping). FD4 was observed in some scratches of the skin and diffused into the epidermis. FITC-OVA was partially observed in the stratum corneum of intact and delipidized skin. In the case of stripped skin, FITC-OVA did not penetrate in the viable epidermis or dermis because it could not pass through tight junctions even if they were open. FITC-OVA was observed in every scratch 2 min after the application and did not diffuse into the surrounding area as FD4 did. It is considered that FITC-OVA penetrates skin defects and remains at the site, which increases the possibility of sensitization by Langerhans cells.