**3. Extraction of essential oils**

*Essential Oils - Bioactive Compounds, New Perspectives and Applications*

wood (agar wood), resin (frankincense), andpetals (rose) [12].

**2. How do essential oils work**

bacterial pathogens [14–16].

used in food and cosmetic industries [17] (**Figure 1**).

mixture of low molecular weight constituents that are responsible for its characteristic aroma, or Essential oils are concentrated liquids of complex mixtures of volatile compounds and can be extracted from several plant organs [8]. The chemistry of EO constituents includes terpenoid and non-terpenoid hydrocarbons and their oxygenated derivatives [5, 9, 10]. Essential oils are concentrated plant extracts that retain the natural smell and flavor, or "essence," of their source Essential oils, also called volatile odoriferous oil, are aromatic oily liquids extracted from different parts of plants, for example, leaves, peels, barks, flowers, buds, seeds, and so on [11]. They may be found in different parts of the plant. Some EOs could be found in leaves (oregano), seed (almond), flower (jasmine), peel (bergamot), berries (juniper), rhizome (galangal ginger), root (angelicaarchangelica), bark (sassafras),

Essential oils include biological compounds like growth factors, hormones, and neurotransmitters that are concentrated from the plant. Several researches have been performed on PEOs in order to confirm their biological efficacy against bacteria and fungi [13]; PEOs have an antibacterial activity where they cause damage to cells via an interface with plasma membrane components which lead to leak the most important compounds and damage the transportation channels, especially of potassium ion [12, 13]. Volatiles from PEOs not only work on single target site in the cell but also they bind to protein structures of the cell. Some of the PEOs and their volatiles are found to be responsible in inhibiting the enzymatic proteins in some

Essential oils used all over the world for disinfection, as anti-inflammatory, relaxing, and stimulating substances, and with potential and modern exploitation in clinical medicine are most commonly used in the practice of aromatherapy, in which they are inhaled, or be swallowed, or can interact with your body in several ways when applied to your skin, some plant chemicals are absorbed also commonly

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**Figure 1.**

*Schematic illustration for the effect of essential oils on bacteria cell. Source: Ref. [10].*

Essential oils are produce from valuable plant products, generally of complex composition including the volatile principles contained in the plant and the more or less modified during the preparation process. The earliest recorded mention of the techniques and methods used to produce essential oils is believed to be that of Ibnal-Baitar (1188–1248). The oil droplets being stored in the oil glands or sacs can be removed by either accelerate diffusion through the cell wall or crush the cell wall [17–20]. The assumed techniques depend on the part of the plants where the oil is to be extracted, the stability of the oil to heat and susceptibility of the oil constituents to chemical reactions. An extract is derived when the plant material is soaked in a substance such as water, alcohol or other liquid for long periods of time so that its flavor, aroma or medicinal properties, infuses into the liquid [11].

Common techniques used for the extraction of essential oils are:

