Synergistic effects have also been observed between essential oils and synthetic antiviral agents. Civitelli and co-workers observed an antiviral synergism between Mentha suaveolens essential oil and acyclovir on HSV-1 [64]. Likewise, Melissa officinalis essential oil potentiated the activity of oseltamivir against avian influenza virus H9N2 [115]. Furthermore, essential oils are lipophilic and therefore may also serve to disintegrate viral membranes [116].