Essential Oils Pharmacological Activity: Chemical Markers, Biogenesis, Plant Sources, and Commercial Products

Secondary metabolites are often among the major players in plants' function, stability, support, bioactivities, defense mechanisms, and therapeutic applications. One of the major components of these metabolites is volatile oils. Essential oils are considered one of the most important ways in which plants express themselves through aroma. The oils are also one of the reasons for therapy, mood-upliftment, life processes, plants and dependent organisms' survival, joy, happiness, aesthetic beauty, and attractions in several realms, as well as for various interactive species, including insects, animals, and humans. In addition, essential oils participate in modern industries and worldwide healthcare systems. Aromatic plants and their extracted and distilled volatile oils have been used in different systems of traditional medicine and in all ancient civilizations. They are also still used as part of modern healthcare systems and in folkloric therapeutic and prophylactic applications. Therefore, the chemistry, bio-based diversity, geographic sources, biological activities, and clinical applications of volatile oils have gained the momentum and continued attention of researchers, culminating in several thousand publications each year. This review provides updated information on the biological activities and current applications of essential oils in medicine and other healthcare uses. The underlined biomechanistic details of the volatile oils' biological effects are also encompassed. The collected data unambiguously supported the biological importance of this class of secondary metabolites, especially in cancer, inflammation, and microbial infection management. The information contained in the data also highlighted the therapeutic importance of these molecules in various aspects of medicine.