**Abstract**

Modern science has tended to use several natural substances that have little or no side effects in daily use or to treat many diseases. Among these materials are essential oils that represent one of the secondary metabolic products of many plants such as Terpenes and Terpenoids, Alkaloids, and the Phenolic compounds, which are extracted by special methods from different parts of the plants. Several applications were using the essential oils such as in the nutrition, cosmetic manufacture, and alternatives to synthetic medication that uses to treatment several infections and diseases as disinfection, as an anti-inflammatory, mouthwashes, as well as in cleaning and calm mood and pesticides. This review describes essential oils, methods of their extraction, and ways of utilization and their application.

**Keywords:** essential oils, extraction, health benefit, antibacterial activity

## **1. Introduction**

Plants produce thousands types of chemicals materials and included two types of metabolites (primary and secondary). Primary metabolites are macromolecules like carbohydrates, fats, proteins, nucleic acids, chlorophylls, hemes this molecular are required for their basic metabolic processes [1] plants, fungi and bacteria of definite genera and families create a number of organic compounds which are not included in primary metabolism that important in essential activity of organism (photosynthesis, respiration, and protein and lipid metabolism) and seem to have no function in growth and development of them [2]. Such compounds are called secondary metabolites (secondary plant products or natural products), there are other name which known as Phytogenic feed additives (PFA) or phytobiotics and botanicals, are commonly defined as various plant secondary compounds (PSC) and metabolites with beneficial effects on animal health and production, including feed and animal products. These compounds are accessary rather than central to the functioning of the plants in which they are found. These compounds are produced in small quantities and their extraction from the plant is difficult and expensive.

There important product of plant secondary metabolites as natural products: Terpenes and Terpenoids (25,000 types), Alkaloids (12,000 types) and the Phenolic compounds (8000 types) [3].

Essential oils (EOs) represent a major group of phytogenic feed additives (PFA). Plant oils and extracts have been used for a wide variety of purposes for many thousands of years [4], Due to their strong aromatic features and bioactivity, EOs have been widely used since ancient times in aromatherapy, as flavor and fragrances in cosmetics and foods, and more recently as pharmaceuticals, natural preservatives, additives, and biopesticides [5–7]. There are many defines of EO, like EO is a

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