Topical gels are a topical drug delivery dosage form commonly used in cosmetics and treatments for skin diseases because of their advantages over cream and ointment. They are formed from a mixture of gelator, solvent, active drug, and other excipients, and can be classified into organogels and hydrogels. Drug formulation and preparation methods depend on the properties of the gelators, solvents, drug and excipients used.

A gel refers to the semi-

solid, 3-dimensional matrix formed from an interspersed system of colloidal particles or the permeation of a solvent into an entwined polymer chain network. Pharmaceutical gels are formed by adding a gelator (gelling agent) to the solvent and active ingredient mixture.

Gelators used in gel formulation can be small molecules with low molecular weight or polymers (synthetic, semi-synthetic or natural). The solvent that is used as a dispersion medium can be aqueous, organic, inorganic, or a system of different solvents.

Topical gels are used as a contact or transport medium for active drugs to act on or through the skin. The active drug molecules are entwined into the 3D mesh of the gel and delivered to the site of action.

Gels have certain special properties that put them apart from other dosage forms, in terms of swelling, syneresis, ageing, rigidity and rheology.

Gels can be classified through a variety of criteria such as their nature of the colloidal phase, nature of the solvent used and physical nature.

This is the most widely used classification of gels. They are classified into two main groups by the nature of the solvent: organogels and hydrogels.