Gels are semisolid systems consisting of dispersions of small or large molecules in an aqueous Liquid vehicle, which has been thickened with a gelling agent. Gels can be a single phase or a biphasic system. 

• Single-phase gels use high molecular weight hydrophilic Polymers as gelling agents. Examples of such polymers include carbomers (cross-linked acrylic acid polymers). These gels are considered to be one-phase systems because no definite boundaries exist between the dispersed macromolecules and the liquid.