RESEARCH ARTI CLE ESSENTI AL OI LS: I TS MEDI CI NAL AND PHARMACOLOGI CAL USES 1* Hamid, A.A., 2 Aiyelaagbe, O.O. and 1 Usman, L.A. 1 Department of Chemistry, University of Ilorin, Nigeria. 2 Department of Chemistry, University of Ibadan, Nigeria. ARTICLE INFO ABSTRACT Essential oils have been important substances since early times. The review of its extraction methods and applications were treated in this study. These include hydrodistillation, hydrodiffusion, effleurage, steam distillation, cold pressing, solvent extraction, microwave assisted process and carbondioxide extraction. Its applications both the medicinal and therapeutics, such as aromatherapy, phytotherapy, antibacterial and antifungal uses, hypolipidemic, antitumor etc. were also reviewed. INTRODUCTION Plants produce primary and secondary metabolites which encompasses a whole array of function (Croteau, 2000). Primary metabolites include amino acids, simple sugars, nucleic acids and lipids, are compounds that are necessary for cellular processes. Secondary metabolites include compounds produced in response to stress such as the case when acting as a deterrent against herbivores. Plants can manufacture many different types of secondary metabolites which have been subsequently exploited by humans for beneficial role in a diverse array of application. Waterman, (1992) suggested that the role of secondary metabolites may centre on the defence of the plants against predation, most especially the herbivores, pathogens or competitor or an acid to pollination or seed disposal or for the protection against or *Corresponding author: hamidmemo@yahoo.com, hamid.aa@unilorin.edu.ng, hamidmemo@gmail.com, adaptation to extrinsic abiotic factors or a combination of these functions. The metabolites may be able to perform roles mentioned above because of their special attributes. These include odour, physiological actions and taste. Secondary metabolites may be referred to as plants natural products. There are three broad categories of plant secondary metabolites as natural products. Terpenes and Terpenoids (25,000 types), Alkaloids (12,000 types) and the Phenolic compounds (8,000 types) (Croteau, 2000). Most of these metabolites have been isolated and characterized. For instance, Madagascan frog of mantellid genus. Mantellid has been a rich source of alkaloid derived directly from arthropods. Eight new phenolic glycosides, cucurbitosides F.M were isolated from the seed of cucurbita pepo. Four sterols and ten triterpenes were isolated from the fruiting bodies of Ganoderma pfeifferi including the three new triterpenes 3, 7, 11-trioxo-5a-lanoster-8-ene-24- diene-26-al (Luciadehyde D, 1), 5a lanoster-8-ene- I SSN: 0975 -833X Available online at http://www.journalcra.com International Journal of Current Research Vol. 3, Issue, 2, pp.086-098, February, 2011 I NTERNATI ONAL JOURNAL OF CURRENT RESEARCH Article History: Received 17 th November, 2010 Received in revised form 12 th December, 2010 Accepted 30 th December, 2010 Published online 11 th February, 2011 © Copy Right, IJCR, 2011, Academic Journals. All rights reserved. Key words: Hydrodistillation, Hydrodiffusion, Effleurage, Phytotherapy, Hypolipidemic.