Palmarosa essential oil inhibits the growth of dandruff-associated microbes by increasing ROS production and...

We investigated the antimicrobial efficacy of seven essential oils from four plant families-Lamiaceae, Asteraceae, Zingiberaceae, and Poaceae-against microbes associated with dandruff. The antimicrobial effectiveness of these essential oils was assessed using paper disk agar diffusion and broth micro-dilution techniques. The results demonstrated that two of the essential oils significantly inhibited the growth of dandruff-associated microorganisms, with inhibition zones ranging from 5 ± 1.81 mm to 29.4 ± 2.70 mm in diameter. Among the tested essential oils, Palmarosa (Cymbopogon martinii) exhibited the highest antimicrobial potency, showing a minimum inhibitory concentration (MIC) between 0.27 and 0.55 mg/mL for the fungi Malassezia furfur and Candida albicans, as well as for the bacterium Staphylococcus epidermidis. The essential oil displayed fungicidal activity within the range of 0.55-2.2 mg/mL and bactericidal activity at 0.55 mg/mL. Additionally, post-treatment effects were evaluated by monitoring the re-growth of fungal and bacterial cells after exposure to Palmarosa essential oil. The results revealed significant retardation of the growth of M. furfur for up to 7 h at 2 × MIC and S. epidermidis for up to 5 h at higher concentrations (1 × MIC and 2 × MIC). The study also found that Palmarosa essential oil-induced reactive oxygen species (ROS) production and altered the integrity of microbial membranes, although it did not impact the concentrations of ergosterol and sorbitol. Regarding safety, topical application of Palmarosa essential oil (at concentrations of 1X, 10X, and 20X MIC) on rats and rabbits caused no irritation, and no sub-acute toxic effects were observed either on the skin or systemically. These promising results suggest that Palmarosa essential oil has the potential to be developed into an effective and safe formulation for treating dandruff associated with microbial infections. Further studies could help solidify its clinical applications.