Cosmetics use lower concentrations of retinol and can cause emerging hypersensitivity reactions as well as redness and irritation of the skin. It is unknown whether the vehicle used in cosmetics may aid in stimulating the inflammatory reaction of the skin, and if the concentration of retinol used could significantly affect the growth of epidermal cells.

A new study published in the Journal of Physiology and Pharmacology evaluated the effects of different concentrations of liquid crystal retinol – 0.15%, 0.3% and 0.5%, on the clinical and histological characteristics of a reconstructed epidermis skin model. In addition, it compared the effectiveness of 0.3% retinol formula in liquid crystal to that in lipid.

The present study used reconstructed human epidermis tissue containing normal human keratinocytes. Here, four original retinol-containing formulas were tested – 0.15%, 0.3% and 0.5% with a liquid crystal base, and 0.3% with a lipid base. Interleukin 6 (IL-6), transglutaminase-1 (TGM1), and epidermal growth factor (EGF) mRNA expression of the skin-equivalent tissue were measured for 10 days of exposure. Histopathological analysis and mRNA quantification were performed. Gene expression was analyzed by total mRNA extraction.

The findings showed that all liquid crystal formulas induced higher EGF mRNA expressions than the lipid base formula. Whereas, IL-6 expression did not differ significantly from the DPBS reference values. On the other hand, GM1 expression was found to increase with the increasing retinol concentration. Furthermore, changes in the epidermal structure were noted—mainly hyperkeratinization of the stratum corneum.

The results suggested that liquid crystal formula might be regarded as more beneficial since it induces less pro-inflammatory action manifested by lowered expression IL-6. Moreover, EGF expression was found to correlate significantly with the retinol concentration of the liquid crystal formula. It was stated that lower concentrations may increase TGM1 expression, thus enhancing the formation of a protective layer of cornified envelope.

Source: Journal of Physiology and Pharmacology. 2020 Feb;71(1). doi: 10.26402/jpp.2020.1.06. Epub 2020 Apr 27.