The mechanism of the synergistic effect of cymene on the
antimicrobial activity of carvacrol is still unknown although the
mechanismof action of both compounds has been extensively studied.
Carvacrol can cause cell death because it can damage the cytoplasmic
membrane, which leads to the collapse of the proton motive force and
depletion of the ATP pool (17). On the other hand, cymene is
ineffective in killing cells because it does not affect the pH gradient
and the ATP pool (17). Having a high preference for cytoplasmic
membranes, cymene can cause swelling of the membrane. Based on
characteristics and mechanisms of action of carvacrol and cymene, it is
possible that the synergistic effect of cymene on the antimicrobial
activity of carvacrol may be because cymene accumulating in and
causing the expansion of the plasma membrane increases transportation
of carvacrol into the cell. However, further investigation is
required for a better understanding of this unclear issue.