The Four Rs of Skin Delivery

By: Johann W. Wiechers, PhD, JW Solutions

Posted: December 9, 2008

"Unknown, unloved" is a well-known expression that applies everywhere and for everything, especially if you cannot see it, because invisibility makes things almost per definition unknown. Take radioactivity, for instance. You cannot see it but it does kill people. The nuclear physicists Marie and Pierre Curie were among the first victims of their own discoveries. But since their pioneering days, we became familiar with the nature of radioactivity and have identified how we can now work safely with radioactive materials. Instead of being classified only as a ruthless killer, radioactivity is now also used in nuclear medicine where it can help save human lives.

A similar situation arises for nanotechnology. We’ve all heard about it but we don’t know what it really entails and we can’t see it, so we classify it as dangerous. Evolution programmed us to fear the unknown in order to survive. This review aims to explain what the implications of nanotechnology in cosmetic science and products are, to eliminate the "unknown" aspect. The review will be in two parts and will focus on the skin delivery aspects of nanotechnology much more than on the principles of nanotechnology and its reputed benefits, although some of them, in particular in sun care, will be mentioned.

Part I, presented here, describes the role of nanotechnology in skin delivery systems in terms of what I call the four Rs of skin delivery. Part II will appear in print in the January 2009 issue of Cosmetics & Toiletries magazine. Part II addresses the fear issue by evaluating experimental skin penetration data on nanomaterials used in cosmetics. Part II also presents a summary and a brief look at the benefits of using nano-sized materials in general and in cosmetics in particular. This knowledge should allow the cosmetic scientist to make a well-informed decision on whether or not to use nanotechnology in his or her products.

Part I begins here with my definition of skin delivery. The definition does not change in the context of nanotechnology and skin delivery. It is: to transport the Right chemical, to the Right site in the skin, at the Right concentration for the corRect period of time.¹ In fact, all skin delivery systems do have an influence on one or more of these four Rs. They may, for instance, affect the right chemical by protecting it and thereby ensure that it will not be an ineffective degradation product that reaches the site of action. They could also impinge on the right site in the skin by targeting the delivery to the site of action of the active ingredient. They could also enhance the skin delivery, thereby ensuring that the right concentration is being used. And finally, they might prolong skin delivery, thereby ensuring that the active ingredient is delivered for a sufficiently long period of time. Please note that I am not saying that all four of these benefits apply for every skin delivery system but if nanotechnology would have any skin delivery benefit, it should influence at least one or more of these four Rs of skin delivery.

Many skin delivery systems actually do use nanotechnology. Dozens of them are listed in the table of contents in Meyer Rosen’s recent book² on delivery systems for personal care and cosmetic products. One could cite liposomes, nanospheres, penetration enhancers, microcapsules, microspheres, stable multiple emulsions, cationic silicone complexes, enzymatically activated encapsulation techniques and many others from Rosen’s seemingly endless list! When I attempted to order such a range of skin delivery systems and functionalities, I finally realized that the functionality of a delivery system is actually following my own definition of the four R’s of a cosmetic delivery system. That is why I will subdivide skin delivery systems as those that affect the Right chemical, the Right site, the Right concentration and the corRect period of time in the following discussion of how nanotechnology fits in with each of these functions of skin delivery systems.