IntroductionEmulsions are a dispersion system composed of two or more immiscible liquids. One of the liquids is dispersed as small fine droplets in the other liquid. Depending on the dispersed and external phases, emulsions can be classified as: water-in-oil emulsions which are fine aqueous droplets dispersed in a continuous hydrophobic oil phase or oil-in-water emulsions which are fine oil droplets dispersed in a continuous hydrophilic aqueous phase. Other types are multiple emulsions consisting of a dispersed phase containing droplets of another phase, for example w/o/woo/w/o. Microemulsions are based on the size of liquid droplets. These include spherical or cylindrical droplets ranging in size from 10 – 120 nm (Mehta, S & Kaur, G 2011) dispersed in another phase using an emulsifier or a mixture of emulsifiers at a high concentration (15 -25%). Emulsions are thermodynamically unstable due to the large surface area between the two phases resulting in high interfacial energy. The system will attempt to lower the energy by reducing the contact area between the two phases resulting in coalescence of the dispersed phase, increase in droplet size and possibly phase separation. Therefore it is important to stabilize the interface between the two immiscible phases. This occurs through the addition of a suitable emulsifying agent. These are amphiphilic surfactants containing both hydrophilic and hydrophobic characters. Therefore they are classified based on the balance of characteristics using the hydrophilic-lipophilic balance (HLB) system. HLB values ​​range from 0 to 20 on an arbitrary scale with each surfactant having a unique value. The higher region of the scale includes hydrophilic surfactants on...... middle of paper ...... sycochemical principles of pharmacy, 4th edition, AT Florence and D.Attwood (eds.), Pharmaceutical Press (2006) , Chapter 4: Drug Stability, pages 93-138.Martin's Physical Pharmacy and Pharmaceutical Sciences, 5th edition, APJ Sinko, Lippincott Williams, and Wilkings (2006), Chapter 15: Chemical Kinetics and Stability, pages 397-434.Francoise Nielloud, F. (2000). Pharmaceutical emulsions and suspensions. [Online access] Google Books. Available at: http://books.google.co.uk/books?id=hDOS5OfL_pQC&printsec=frontcover&dq=emulsions&hl=en&sa=X&ei=AnVeU- r0NsnF7Ab8qYG4CQ&ved=0CFUQ6wEwBg#v=onepage&q=emulsions&f=falseDipak Kumar, Sarker. (2013). Pharmaceutical Emulsions: A Drug Developer's Tool Bag. [Online access] Google Books. Available at: http://books.google.co.uk/books?id=XHgoAgAAQBAJ&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false