The mystical effects of dermatological vehicles.

Topical treatment of the skin is as old as the evolution of man. Instinctively, we try to treat a skin injury or irritation with cooling or soothing substances. Even animals lick their wounds, trusting instinctively in the healing power of saliva. When did this archaic pattern of treatment take the gigantic leap from folk medicine to modern drug therapy? This text illustrates the evolution of topical dermatological vehicles, their application (guidelines) and future use. In particular, a phenomenon that has so far been ignored in product development and clinical testing is the vehicle metamorphosis. In clinical and experimental situations, most dermatological vehicles undergo considerable changes after they have been removed from the primary container and are applied to the skin. Subsequently, the initial structural matrix, and the quantitative composition of the vehicle, will most likely change during and after the mechanical shear associated with application of the product and/or evaporation of ingredients. This natural, but highly dynamic process will generate mini-environments for the active moiety that are difficult to predict and that are crucial to the fate of the active moiety. Despite the reasonable wishes of formulators, clinicians, patients and customers, there are still no universal vehicles. Each drug, at each concentration, requires a different vehicle for optimized therapy. Stability and compatibility of excipients and active moiety are crucial for any commercially available pharmaceutical or cosmetic formulation, together with local and systemic safety of all components. Nonetheless, more diverse and molecularly complex classes of new dermatological vehicles are continuously being researched and refined. The scientific progress has been remarkable when one considers the simple emulsion mixtures that were commonplace in dermatological therapy and still persist to this day in commercial products. It is to be hoped that the result of these research endeavors will be the emergence of more innovative topical formulations, applying engineered bioavailability control systems, with broader applications in topical therapeutic and cosmetic vehicles.