Natural products derived from medicinal plants play increasingly important roles as alternative antifungal and anticancer agents. The aim of this study was to assess the cytotoxic and genotoxic effects of tea tree, thyme, peppermint and clove essential oils against two model organisms, namely, the fungal pathogen Candida albicans and cancer HeLa cells. The chemical compositions of the tea tree and peppermint oils predominantly comprised terpene alcohols, and the major constituents of the thyme and clove oils were phenolic compounds. Our results indicated the ability of all tested essential oils to disrupt the permeability barrier of cell membrane structures, which was the most likely the cause of their lethal action against Candida albicans, as well as damage of mitochondria and DNA in the HeLa cells. None of the evaluated essential oils inhibited the synthesis of fungal cell wall. Although the essential oils were characterized by different chemical compositions, they affected the same cellular targets, indicating that these cytotoxic and genotoxic effects can be considered to occur by the same universal mechanism. We assumed that this multidirectional activity of the various essential oils was due to their complex nature rather than the presence of any one particular compound.