Multifaceted amelioration of cutaneous photoageing by (0.3%) retinol

Background Although retinol skin care products improve the appearance of photoaged skin, there is a need for an effective retinol concentration that provides skin benefits without irritation. Objective To compare the efficacy of topical 0.1%, 0.3% and 1% retinol in remodelling the cutaneous architecture in an in vivo experimental patch test study, and to determine tolerance of the most effective formulations when used in a daily in‐use escalation study. Methods For the patch test study, retinol products were applied under occlusion, to the extensor forearm of photoaged volunteers ( n = 5; age range 66–84 years), and 3 mm skin biopsies obtained after 12 days. Effects of different retinol concentrations, and a vehicle control, on key epidermal and dermal biomarkers of cellular proliferation and dermal remodelling were compared to untreated baseline. Separately, participants ( n = 218) recorded their tolerance to 0.3% or 1% retinol over a six‐week, approved regimen, which gradually increased the facial applications to once nightly. Results Retinol treatment induced a stepwise increase in epidermal thickness and induced the expression of stratum corneum proteins, filaggrin and KPRP. 0.3% retinol and 1% retinol were comparably effective at inducing keratinocyte proliferation in the epidermis, whilst reducing e‐cadherin expression. Fibrillin‐rich microfibril deposition was increased following treatment with 0.3% and 1% retinol ( p < 0.01); other dermal components remained unaltered (e.g., fibronectin, collagen fibrils, elastin), and no evidence of local inflammation was detected. The in‐use study found that 0.3% retinol was better tolerated than 1% retinol, with fewer and milder adverse events reported (χ 2 (1) = 23.97; p < 0.001). Conclusions This study suggests that 1% and 0.3% retinol concentrations were similarly effective at remodelling photodamaged skin in an in vivo model of long‐term use. Use of 0.3% retinol in the escalation study was associated with fewer adverse reactions when applied daily. Hence, 0.3% retinol may be better tolerated than 1% retinol, thereby allowing longer‐term topical application.