In Vitro Anti-Malassezia Activity of Castanea crenata Shell and Oil-Soluble Glycyrrhiza Extracts

BACKGROUND: A new shampoo with anti-Malassezia properties obtained from various plants is required to provide seborrheic dermatitis patients with a wider range of treatment options. OBJECTIVE: The aim of this study was to obtain in vitro susceptibility profiles of Malassezia restricta and M. globosa, the most important pathogenic organisms in the development of seborrheic dermatitis, to the plant extracts used in commercial anti-dandruff shampoos. METHODS: Minimal inhibitory concentrations (MICs) were determined for eight candidate plant extracts and two plant-derived natural products diluted with Leeming and Notman medium to final concentrations of 0.016 to 1 mg/ml. RESULTS: Castanea crenata shell, Camellia sinensis leaf, and oil-soluble Glycyrrhiza extracts presented relatively low MIC values (≤0.5 mg/ml) against both strains. The C. crenata shell and oil-soluble Glycyrrhiza extracts demonstrated especially high anti-Malassezia activity, suggesting their potential use in the treatment of seborrheic dermatitis. The extracts also showed fungistatic activity against other common facultative pathogenic yeasts, Cryptococcus and Candida. CONCLUSION: C. crenata shell and oil-soluble Glycyrrhiza extracts could potentially be used as active ingredients in anti-seborrheic and anti-dandruff shampoo formulations. They could be helpful for repeated treatments and regular prophylaxis of scalp seborrheic dermatitis.