What are the essential oils?

I have seen several people have confused with the definition of essential oils. CO2 extracts, absolutes, concretes, and carrier oils are assumed or sold as essential oils in the market. So in this post, I will try to define essential oils precisely.

According to Harrewijn et al. (Harrewijn, van Oosten and Piron, 2000), essential oils are complex mixtures of volatile compounds that are produced by living organisms and isolated by physical means, such as pressing and distillation, from a whole plant or plant portion of known taxonomic origin. Controversy surrounds the definition of essential oils from distillation (Sadgrove and Jones, 2015). Therefore, the ISO (International Organization for Standardization) has defined a universally accepted definition for essential oil as, “Products obtained from natural raw material, either by distillation with water and steam, or from the epicarp of citrus fruits by mechanical processing, or by dry distillation” (Schnaubelt, 1999; International Organization for Standardization, 2013).

               Essential oils are stored in specialized cells/glandular cells or organelles within any plant tissue. The first recorded method of extracting essential oils was written by Andalusian physician and chemist Ibn al-Baitar in the 13th century (Firenzuoli et al., 2014). Modern techniques rely on pressing, rubbing, or heating particular regions to rupture the cells and release the aromatic compounds. Therefore, essential oils are mostly obtained by cold pressing, steam distillation, and hydrodistillation.

           The essential oil components are mainly produced from four major biosynthetic pathways: (1) the mevalonate pathway leading to sesquiterpenes and triterpenes, (2) the methyl-erythritol-pathway leading to mono- and diterpenes, (3) the shikimic acid pathway yielding phenylpropanoids, and (4) the acetate pathway for fatty-acid derived compounds. With only these pathways, there are still large numbers of compounds with tremendous variation within the composition of essential oils (Kubeczka, 2010).

Essential oils (EOs) have a rich history and are of great importance in traditional medicine all around the world. The World Health Organization (WHO) defined traditional medicine as “the sum total of the knowledge, skills, and practices based on the theories, beliefs and experiences indigenous to different cultures whether explicable or not, used in the maintenance of health as well as in the prevention, diagnosis, improvement or treatment of physical and mental illness” (World Health Organization, 2015). Based on this definition, one can appreciate the vast importance of traditional medical systems globally. On the Indian subcontinent, essential oils have a profound impact on the Ayurvedic “Gandhshastra”—the science that deals with flavor and fragrance (NIIR Board, 2004).

In Hindu mythology, there is a famous mantra, "सुगन्धिं पुष्टिवर्धनं, Sugandhim Pushtivardhanam.

"Sugandhim: Means fragrance. Like a spreading fragrance, all of this permeates the whole of existence, while at the same time being that existence. Pushtivardhanam: Means that which sustains and nourishes all. Thus, the fragrance that permeates all is the sustainer of all beings while also the essence of all beings."Reference

According to the Egyptian Ebers Papyrus manuscript from around 1550 B.C., ancient Egyptians were the first to identify the therapeutic potential of botanical extracts (Brumer, 2014). They also used these extracts for flavor and fragrance during religious ceremonies in temples and pyramids. In the Chinese herbal tradition, dating back 4,000 years, aromatic materials were used as therapeutic agents (Tang et al., 2009). Aromatic botanical materials have also repeatedly been mentioned in many Judeo-Christian and Muslim religious texts (Singh and Hamal, 2013).