Abstract
Retinol, an established topical ingredient for improving signs of photo-aging, is often limited in concentration due to the potential for low-level visible and sensory signs of irritation. A new anhydrous, 0.5% stabilized retinol serum was developed, balancing bioactivity and tolerability. This patented formula uses the Relative Polarity Index (RPI) between skin, retinol, and emollient ratios, allowing for controlled bio-delivery of retinol to skin. The product also includes skin-smoothing emollients, and antioxidants to stabilize the retinol. Retinol bioactivity and tolerability were first evaluated through gene and protein expression using human skin explants. Gene expression results indicated significant induction of genes with anti-aging benefits, such as cellular retinoic-acid binding protein-2 (CRABP2), a highly sensitive marker of retinoid bioactivity, Heparin-binding EGF-like growth factor (HBEGF), and hyaluronan synthase-3 (HAS3). Additionally, minimal to non-significant induction of IL-8, an inflammatory irritation marker, was observed compared to untreated controls. Histology results also demonstrated significantly increased collagen production. To further evaluate irritation potential, a clinical modified cumulative patch model was developed to differentiate irritation of retinol products. The new 0.5% retinol serum was found to have significantly less irritation (p<0.05) versus a competitive in-market 0.5% retinol formulation. A 4-week clinical in-use test was performed to assess the facial tolerance and self-perceived efficacy of the serum. Study results concluded daily use was well-tolerated, with no statistically significant increases (p<0.05) in tolerance parameters. Moreover, self-perception questions yielded positive results for improvements on visible aging attributes, confirming our ex vivo results. This new 0.5% retinol serum delivers bioactive retinol to target advanced visible signs of aging, without the increased irritation.
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