Abstract
The global escalation of antifungal drug resistance, combined with the toxicity and environmental persistence of synthetic fungicides, has created an urgent need for natural, multi-mechanism alternatives. This study presents the first systematic comparative evaluation of three commercially relevant essential oils cinnamon (Cinnamomum zeylanicum), lemongrass (Cymbopogon citratus), and tea tree (Melaleuca alternifolia) individually and in defined binary and ternary combinations, against four clinically significant fungi: Candida albicans, Trichophyton rubrum, Microsporum gypseum, and Malassezia furfur. Antifungal activity was assessed by agar well diffusion, broth microdilution for minimum inhibitory concentration (MIC), checkerboard titration for fractional inhibitory concentration index (FICI), time-kill kinetics, and FTIR spectroscopy for mechanism elucidation. Individual MICs ranged from 0.078% to 0.625% (v/v); cinnamon oil was the most potent against C. albicans (MIC 0.078%), tea tree oil against M. furfur (MIC 0.078%), and all three oils showed equivalent MICs (0.156%) against dermatophytes. Binary combinations produced selective synergy: the lemongrass + tea tree pair against C. albicans (FICI 0.50), cinnamon + lemongrass and cinnamon + tea tree against T. rubrum (FICI 0.50 each), cinnamon + lemongrass against M. gypseum (FICI 0.50), and the cinnamon + tea tree blend against M. furfur (FICI 0.312 strong synergy). The ternary blend (1:1:1 ratio) achieved universal synergy across all four fungi, with FICI values of 0.25–0.375 and total inhibitory concentrations as low as 0.039% a 16-fold dose reduction versus monotherapy. Time-kill assays against C. albicans confirmed rapid fungicidal activity, with >3-log10 reduction in colony-forming units achieved within 8 hours and complete sterilisation by 24 hours. FTIR spectroscopy of treated C. albicans cells revealed a multi-target mechanism of action: marked reductions in protein Amide I and II bands, near-complete obliteration of cell wall polysaccharide bands (1070–1240 cm⁻¹), and membrane lipid disorder. These converging lines of evidence establish the ternary essential oil combination as a potent, rapid-acting, multi-mechanism antifungal candidate with potential for development into topical herbal formulations for the management of dermatomycoses.