Essential Oils and the Emerging Demand for Synergy among Compoundsin the Biological Field

Essential oils (EOs), a mixture of natural volatile compounds produced by aromatic plants as secondary metabolites in response to pathogen- and herbivore-induced challenges, have been explored for their anthropocentric advantages. The different constituent compounds work as a suite in the bulk oil, and their versatile properties as insecticidal, antimicrobial, antiinflammatory, antifungal, and flavoring agents are well-documented in scientific literature. In recent times, the demand for EOs and their compounds has grown in different industrial sectors. The development of resistance in pests and pathogens to single-compound pesticides and drugs has heightened the importance of synergistic combinations in biological fields. Accordingly, research in the field is gaining momentum to develop synergistic products that are effective at low doses, long-lasting, delay resistance, and cause minimal side effects. This review aims to comprehensively present the published research findings on potential combinations in the healthcare and agricultural sectors that use EOs and compounds, and to understand the mechanisms behind synergies. For this, databases such as PubMed, ScienceDirect, and Google Scholar were used for searching published articles using the keywords “combination therapy”, “essential oil and its compounds”, “synergism”, “mechanism of action”, “anti-microbial resistance”, “insecticide resistance”, “plant secondary metabolites”, and “nanocarriers”. The existing literature highlights essential oil(s) and their constituents as effective and relatively safe, with synergistic properties and diverse mechanisms of action. This opens up scope for developing novel, optimized products or formulations in the future by combining them in specific ratios or with existing commercial drugs/antibiotics/pesticides, to be used sustainably in the pharmaceutical/agricultural sectors. The information on composition, structure, and mode of action of constituents would help in achieving an effective product for therapeutic or pest management interventions.