Cosmetiscope - October 2016

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OCTOBER 2016 • Vol. 22 No. 8

New York Society of Cosmetic Chemists

www.nyscc.org

Solids and Nanoparticles: Interactions with the Skin

M

…by Nava Dayan

any compounds incorporated into topical formulations are in their solid particulate form. Examples include zinc oxide in diaper rush ointment or in calamine lotion for chicken pox, and sunscreens containing both titanium and zinc oxide, as well as other powders such as mica and pigments. Some of these formulations are intended to treat and alleviate symptoms of irritation in partially compromised skin, while others, such as sunscreens or optically active powders, are intended to be applied to healthy intact skin and act merely on the very upper layer (no penetration needed) to protect from radiation or create an even-tone appearance, respectively. Some powders are incorporated for an enhancement of appealing sensation. When assessing potential routes for penetration into the skin, the following can be outlined: • Via the intercellular lipids; • Via the corneocytes; and • Via the follicular route. The intercellular skin lipids (located between corneocytes) are composed mainly of hydrophobic ceramides, long chain fatty acids, cholesterol, and cholesterol derivatives. They are organized in a gel crystalline rigid structure to control penetration. In 2003, Phil Wertz and Jennifer Hill published a paper describing molecular models of the intercellular lipid lamellae from epidermal stratum corneum.1 Their work examined electron density profiles measured from transmission electron micrographs of porcine stratum corneum prepared using ruthenium tetroxide. Dense band center-to-center measurements were consistent with a 5-3–5 nm arrangement; correlating to 13 nm band distances in the lamellar structures in between the corenocytes in the stratum corneum. This was clearly a very important finding with implications to skin barrier health; however, it is not clear if Wertz and Hill’s research suggests that

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unless a particle is on the low end of the nanometer scale, it will not partition into the stratum corneum. Most compounds partitioning into the skin are known to intercalate via the intercellular lipid lamellae; however, penetration via keratinized corneocytes is most likely to occur as well. Corneocytes are polyhedral, anucleated entities without cytoplasmic organelles, interlocked with each other and organized as vertical columns of 10-30 cells. As noted, they are embedded within a highly hydrophobic lipid matrix to form the stratum (Continued on page 2)

P R O F E S S I O N A L D E V E L O P M E N T S Y M P O S I U M October 6 • New Brunswick, New Jersey


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