Abstract
Essential oils are valuable natural products extracted from flowers, leaves, fruits, fruit rinds seeds, stems, roots, barks, or resins of various plants. They are used as raw materials in many fields, including perfumes, cosmetics, spices, foods, nutrition and treatment for several health disorders. Essential oils are complex mixtures comprising many single compounds. There are several methods for extracting the essential oils. Various researchers reported biological activities of essential oils. However, activities of the same essences are different from the extracted oils. This variation could be understood by studying the factors which influence the chemical composition of the essential oils, in particular under photochemical conditions. This review discusses the major components present in the essential oils, the methods of extraction from plants, stability, photochemical reactions of essential oil and their important components under different conditions and biological activities of essential oils.