Nonionic Surfactants: Polyethylene Glycol (PEG) Ethers and Fatty Acid Esters as Penetration Enhancers

Polyethylene glycols (PEGs) are a wide family of synthetic polyethers available in a range of molecular weights. Due to their multifunctional properties, PEGs are used both as such and/or in the form of nonionic derivatives in the formulation of cosmetics and medical products. In consideration of their physicochemical characteristics, they can penetrate into the intercellular regions of the stratum corneum, increase the fluidity and solubilise lipid components as well as bind to keratin filaments causing a disruption within corneocytes. In the current chapter, the performances of PEG ethers and esters as penetration enhancer are discussed according to the referenced literature underlining the influences of the physicochemical properties of surfactants (i.e. functional groups, size of the polar head groups, polyoxyethylene chain length, alkyl chain length, degree and position of unsaturation and the hydrophile–lipophile balance) on the penetration of chemicals incorporated in various types of formulations, such as parenteral, topical, ophthalmic, oral and rectal formulations.