The selection of active ingredients for topically applied formulations requires scientific knowledge in physicalchemistry and biochemistry. This 3-day intensive course is intended to help becoming familiar with the fundamentals of skin physiology, structure, renewal, aging process, UV response and the like, to identify those physiological steps, which are accessible to topically applied substances. Becoming familiar with these subjects will allow one to envision the possible interactions between a topically applied formulation and the skin as a viable organ. This can allow for optimization of products. This course will provide participants with elements leading to the understanding that topically applied products can measurably, visibly and quickly affect the skin. To achieve this result a formula has to be “built” around the active to be delivered, by avoiding those ingredients, which might interfere with the proper delivery. Examples of different efficacy for the same ingredient in different formulas will be provided.