238 Retinol at a concentration of 0.3% restores fibrillin-rich microfibrils and modifies the epidermis in photoaged human skin in vivo in a manner similar to 1% retinol

Whilst retinol concentrations of 1% weight/volume (w/v) in skincare cosmetics are commonplace within the US market, lower percentage formulations are associated with fewer tolerance issues. Here we investigated the effect of retinol at 0.1%, 0.3% and 1% w/v upon epidermal barrier, keratinocyte proliferation and deposition of fibrillin-rich microfibrils (FRM) in a 12-day in vivo patch test. The vehicle control (VC) and retinol formulations were applied under occlusion to photoaged forearms of healthy volunteers (n=5; 66-84 years) prior to biopsy and analysis of key biomarkers of skin health. Epidermal thickening occurred in response to 0.1% retinol (mean ± SEM; 81.62 μm ± 8.5), 0.3% retinol (92.7 μm ± 8.2) and 1% retinol (122.3 μm ± 31.2) compared to untreated, occluded forearm (baseline; 42.3μm ± 4.8) and VC (42.36 ± 3.5). Statistical significance however, was only reached in response to 0.3% retinol (p<0.05). Deposition of papillary dermal FRM, known to be diminished in photoaged skin, was significantly restored after treatment with 0.3% (a.u., mean ± SEM; 3.36 ± 0.1; p<0.05) and 1% retinol (3.31 ± 0.2; p<0.05); 0.1% retinol (2.95 ± 0.26) and VC (3.06 mean ± 0.2) failed to induce significant changes above the baseline (2.32 ± 0.2). All retinol concentrations increased keratinocyte proline-rich protein deposition within the stratum granulosum and induced keratinocyte proliferation, concomitant with loss of e-cadherin expression at the basal layer. These data suggest that a retinol concentration of 0.3% appears to have similar efficacy to 1% retinol in its ability to modify the epidermis and restore the FRM network.