Skin Penetration of Fatty Acids from Soap Surfactants in Cleansers Dependent on Foam Bubble Size

Carbon dioxide foam bubbles enhance skin penetration through the stratum corneum layer with mechanical mechanism

Topical skin formulations often include penetration enhancers that interact with the outer stratum corneum (SC) layer to chemically enhance diffusion. Alternatively, penetration can be mechanically enhanced with simple rubbing in the presence of solid particles sometimes included to exfoliate the top layers of the SC. Our goal was to evaluate micron-sized carbon dioxide bubbles included in a foamed moisturizing formulation as a mechanical penetration enhancement strategy. We show that moisturizing foam bubbles cause an increase in SC formulation penetration using both mechanical and spectroscopic characterization. Our results suggest viscous liquid film drainage between coalescing gaseous bubbles creates local regions of increased hydrodynamic pressure in the foam liquid layer adjacent to the SC surface that enhances treatment penetration. An SC molecular diffusion model is used to rationalize the observed behavior. The findings indicate marked increased levels of treatment concentration in the SC at 2 h and that persists to 18 h after exposure, far exceeding non-foamed treatments. The study suggests an alternate strategy for increasing formulation penetration with a non-chemical mechanism.

Friction Dynamics of Foaming Body Cleansers under Sinusoidal Motion

The friction characteristics of foaming body cleansers determine skin physical irritation, as well as the usability of the products. In this study, the friction of foam formed by a commercial body cleanser was evaluated using a sinusoidal-motion friction evaluation system. The friction profile of the foam was a hydrodynamic stable pattern, where the friction force increased with increasing velocity. In addition, soapbased cleansers, containing polyols, showed large friction coefficients. These properties suggest that the mechanical properties of the interfacial film and viscosity of the cleanser bulk affect friction properties. These findings assist in controlling the texture of body cleansers.