Polypeptides comprising arginine and lysine regulate the microbial balance in seborrheic dermatitis

Malassezia furfur (Mf) and Staphylococcus aureus (Sa) are the causative microorganisms of seborrheic dermatitis (SD). Notably, Staphylococcus epidermidis (Se) inhibits the growth of Sa and secretes moisturizing components. Therefore, suppression of Mf and Sa proliferation and promotion of Se growth are crucial to mitigate SD. We previously reported that a mixture of hinokitiol and maltotetraose-containing oligosaccharides (MTO) at varying concentrations inhibits the growth of Mf and Sa or inhibits the growth of Mf while promoting the growth of Se. In this study, we aimed to assess the effects of the three aforementioned microorganisms using reagents with purported antibacterial or antifungal properties, namely ferulic acid, succinic acid, polylysine, and peptiskin (PK: Arginine and lysine polypeptide), to evaluate their efficacy in improving the scalp microorganisms associated with SD and determine their effective concentrations. Additionally, we evaluated the combined effects of MTO, a previously reported Se growth-promoting agent, and the effective agent identified in this study. Notably, 0.08% PK was the sole reagent significantly reducing and inhibiting the proliferation of Mf and Sa, respectively, while significantly increasing that of Se. Moreover, 0.80% PK and 1.40% MTO combination significantly promoted Se proliferation compared to 0.08% or 0.80% PK alone. Overall, our results highlight the potential of PK, either alone or in combination with MTO, to prevent and treat SD.