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Exploring the Depths of Percutaneous Penetration
By: Elsa Jungman, Université Paris-Sud
Posted: July 3, 2012
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For Gummer, cosmeceuticals are an “itch that won’t go away.” As he explained, for him, a product can be either a cosmetic or a medicine; there is no middle ground. Cosmeceuticals are borderline products that are not clear. Gummer explained that the US Food and Drug Administration, and UK and Australia guidelines do not recognize the term cosmeceuticals; only Japan recognizes them as “quasi-drugs.” Some products claim, for example, to work against hair loss with no side effects. However, according to Gummer, this is not possible because if a product works, there are effects; if not, it does not work. So for Gummer, “Cosmeceuticals exist in the advertising world,” because they cannot be defined and regulations need to fast-track these borderlines products. He concluded that it would be in the industry’s best interest “to make cosmeceuticals go away.”
A special lecture was presented on the concept of barrier, skin penetration and beyond with a look at concepts presented from 1850–1980 by Robert Scheuplein, PhD, of Keller and Heckman. Scheuplein is an international expert on risk assessment who worked for nearly 20 years at the US FDA. His mentors were Irvin Blank and Albert Kligman, who introduced him to skin permeation and medical/biological research on skin.
Scheuplein explained that between 1850 and the 1860s, the fact that there was a barrier in the epidermis was discovered but it took around one hundred years to locate it in the stratum corneum. Kligman showed that the stratum corneum was stiff by placing it on the top of a bottle full of water, and even with the bottle turned upside-down, the water was contained. In this way, Kligman demonstrated that the stratum corneum was impermeable to water.
Blank demonstrated that water could remain in the stratum through the use of tape-strips. After eight strips, he found transepidermal water loss (TEWL) to increase significantly. The tape-stripping technique was introduced by Wolf, and showed precisely the location of the barrier zone in the stratum corneum.
Two decades of work determined that the principal barrier layer of the skin is the bulk of the stratum corneum. Studies also showed that the skin does not behave like a passive diffusion medium; it was demonstrated that the stratum corneum/epidermis or full thickness skin has the same permeation rate as whole skin. However, this was not the case for the permeation rate of exogenous chemicals. The effect of the vehicle was also a great discovery. Diffusion was tested and an increase in the transepidermal flux with, for example, water or methanol as a vehicle was observed. However, lipophilic solvents tended to decrease the flux.