APPLY TOPICALLY: A Practical Guide to Formulating Topical Applications

Abstract

The main objective of Pharmaceuticals and Skin care Development is to create effective products based on the state-of-the-art active ingredients with improved patient compliance and usability. Thus, the vehicle/carrier used to delivery topical active ingredients through the skin layers and mucous membrane, can considerably influence the performance of the actives’ effectiveness. The carrier can have direct effects on both skin and mucous membrane barrier, as well as it can enhance or retard the delivery of the active agent(s) to the target site of action. In addition it can affect the skin and mucous membranes appearance and the relative sensory properties of the final formulation, often influencing the patient compliance. Skin and mucous membranes (MB) are, in fact, the first line of the human body’ defence and, acting as a biological barrier, offer thermal insulation, prevent water loss, and protect the internal organs from the external environment, foreign toxic substances, and pathogens. Skin, generally less than 2 mm thick, is composed of several layers, the outermost of which the stratum corneum (SC) (10-30um thick) represents the primary barrier. On one hand, SC is composed of corneocytes filled with keratin filaments enclosed by an envelop of cross-linked proteins, and surrounded by a semi continuous matrix of lipids, which create a strong biological barrier. On the other MBs, covered by adhesive gel-like mucus and composed of a densely woven network of natural mucin polymers interspersed with a variety of glycoproteins, create another effective barrier to diffusion across mucosal surfaces. Both the Skin lipids -organized in lamellar fashion and produced/secreted during the maturation of the keratinocytes and mucus, constantly secreted and turned over, represent strong cellular and molecular barriers to penetration of any kind of compounds. Therefore the necessity to overcome these barriers by the use of right vehicles which, able to disturb the lipid structure within the stratum corneum and/or the mucus molecular organization within MB can increase the permeability of the active ingredients through these structures.