Why has this article been titled “Formulation Fantasies”? Numerous examples of claims that are made in the popular press misrepresent the facts about formulations used on the skin for personal care, and cosmetic science is not well-served by this misinformation. Here, the authors examine a number of such statements, specifically that:
1. 60% of a material placed on the skin is absorbed;
2. liposomes and nanoparticles penetrate skin;
3. there are generic, “do all” formulas;
4. the nature of the formulation does not affect permeation; and
5. it is possible to target different strata of the skin.
In relation, also discussed is the need for rational design of preparations for application to the skin.
60% Absorption?
Perhaps the first of these above statements is the most often quoted. A simple search on the Internet for the terms beauty products and skin will reveal: “Even manicures and pedicures should be avoided because studies show that you absorb through your skin about 60 percent of whatever you put on it. Some of these things can be full of harsh chemicals that are bad for your overall health and especially your baby.”1 Also, “Your skin—the body’s largest organ—absorbs up to 60 percent of the products you put on it every day, from soaps to shampoos to sunscreens. Considering that most of us use about 10 different products daily, that can really add up.”2
In fact, as most cosmetic scientists know, the skin has evolved to keep water in and other xenobiotics or foreign substances out. The outer layer, i.e., the stratum corneum (SC), is a unique membrane that is about a sixth of the thickness of a piece of paper. It is composed of dead cells that are filled with keratin and are very dense in nature. The cells overlap, as in a brick wall (see Figure 1), and the mortar that surrounds them is a complex mixture of lipids organized into bilayer arrays.
