~ 1 ~ American Journal of Essential Oils and Natural Products 2019; 7(4): 01-10 ISSN: 2321-9114 AJEONP 2019; 7(4): 01-10 © 2019 AkiNik Publications Received: 02-08-2019 Accepted: 09-09-2019 R Soulimani Université de Lorraine, LCOMS/ Neurotoxicologie Alimentaire ET Bioactivité, Campus Bridoux, Metz, France J Bouayed Université de Lorraine, LCOMS/ Neurotoxicologie Alimentaire ET Bioactivité, Campus Bridoux, Metz, France Rakesh Kumar Joshi Lecturer Chemistry, Department of Education, Government of Uttarakhand, India Correspondence: R Soulimani Université de Lorraine, LCOMS/ Neurotoxicologie Alimentaire ET Bioactivité, Campus Bridoux, Metz, France Limonene: Natural monoterpene volatile compounds of potential therapeutic interest R Soulimani, J Bouayed and Rakesh Kumar Joshi Abstract The majorities of essential oils are extracted from aromatic and essential plants and have been used in their natural state for millennia for many applications. They consist of bioactive ingredients (terpenes) known for many biological properties. Their physicochemical characteristics classify them as volatile and fragrant natural organic compounds (FOCs) and play an important role in Plante-Animal communication, in the defense of plants and forests against natural aggressions, but also to fight against drought by contributing rain. It is important to distinguish FOCs from VOCs (volatile organic compounds) synthesized or produced from petrochemical derivatives or from purified natural compounds and have real potential adverse effects. We carried out this review to list the different works carried out on the essential oils rich in one of the most known and used natural compounds (Limonene) in order to highlight its beneficial properties and its possible harmful effects by specifying the various conditions of studies. It is also important to emphasize the difference between volatile organic contaminants (VOCs), which are generally pollutants resulting from human activity or the synthesis or purification of molecules, and fragrant organic compounds (FOCs), whose ratio benefit risk is more in favor of their use with a good control of the recommendations on the doses of use. Keywords: VOCs, (FOCs), limonene, pharmacology, toxicology, terpenes, risk/benefit 1. Introduction Limonene is a ubiquitous terpene that is found, among others, in essential oils of lemon tree, orange, neroli, bergamot, and tangerine. Limonene is one of the major constituents of citrus peel, and its presence in the citrus peel contributes to their smell. Limonene is a monoterpene formed from two isoprene units, which are five-carbon molecular building blocks. Limonene exists as two enantiomers, d-limonene and l-limonene. The more common d-enantiomer has a strong smell of oranges; however, in the presence of aird-limonene can be slowly oxidized [1] . For industrial purposes, d-Limonene is recovered from citrus fruits through two primary processes namely steam distillation and centrifugal separation. It is commonly used as a base ingredient in the manufacture of cleaning products as a solvent; and is also used in chemical synthesis as a p-cymene carvone precursor [2] . Natural limonene has a pleasant more like lemon scent, making it widely used as a flavor and fragrance additive in common foods, such as fruit juices, candies, chewing gums, soft drinks and ice creams. Limonene is one of the most common fragrances used in the formulation of cosmetics, and can be found in many types of beauty products such as soaps, perfumes, shampoos, hair conditioners and shower gel, cleaners and biocides. In addition, limonene is considered safe for food preservation and could be used as a green solvent for the extraction of natural products. Limonene can be also of synthetic origin. Since the 1990s, the annual world production of d-limonene and orange essential oil (95% d-limonene) has exceeded 45 kilotons. This molecule plays an important role in the composition of these essential oils and helps to reduce the irritating action of citrals (also present in these essential oils). 2. Physico-chemical properties The molecular structure of d-limonene consists of 10 carbon atoms and 16 hydrogen atoms: (C10H16).