Skin aging is a major consideration regarding cosmetic skin care. The cosmetic field is seeking new active ingredients able to slow down the appearance of signs of age. Some lichens and more specifically the genus Cetraria s. str. presents an interest as a source of active molecules because it is already being used in traditional and modern medicines. To better evaluate the potential of C. islandica as anti-aging skin care, we investigated some key aspects to protect skin from external aggression and to avoid skin alteration, which would exacerbate signs of age. Among them, our results reveal (i) antioxidant capacities; (ii) anti-inflammatory properties on human keratinocytes once stimulated, as shown by a decrease in IL-6, IL-8, CXCL9, CXCL10, and CCL5; (iii) a downregulation of MT1-MMP, which corresponds to decreased tissue remodeling; and (iv) an inhibition of human tyrosinase, which could correct the appearance over time of age-related skin spots. Altogether, these results highlight the potential use of C. islandica in anti-aging skin care.

In vitro enzyme inhibition assays are widely used to substantiate anti-ageing and depigmentation claims for cosmetic ingredients, yet acidic formulations can suppress enzymatic activity through pH alone, independently of any active ingredient. This study evaluated the antioxidant, enzyme-inhibitory, and cytotoxic properties of three aqueous hair care formulations (HS-W, HS-W-CGO, HS-W-CG; pH 4.0–4.5) and assessed whether observed inhibition reflects genuine bioactivity or pH-mediated artefact. Total antioxidant capacity (TAC) was determined by copper-reduction colorimetry. Elastase and collagenase inhibition were evaluated with fluorescently labelled substrate kits. Human tyrosinase inhibition was assessed using a cell-lysate-derived Homo sapiens tyrosinase (hsTYR) assay with kojic acid as positive control and a pH-matched citrate buffer as vehicle control. Cytotoxicity was measured in HaCaT keratinocytes by AlamarBlue® assay at 24 h and 48 h. TAC was low across all formulations (HS-W: 23.2 ± 5.8; HS-W-CGO: 16.4 ± 7.0; HS-W-CG: 2.8 ± 1.0 µM TE), consistent with the ester-blocked activity of tocopheryl acetate. Elastase inhibition was negligible. All three formulations showed apparent collagenase (IC₅₀ ~3–4% v/v) and hsTYR inhibitory activity (IC₅₀ ~2% v/v); IC₅₀ values were indistinguishable across compositionally distinct formulations, and the citrate buffer yielded a comparable inhibitory profile, providing dual evidence for a pH-driven rather than ingredient-specific mechanism. Dose-limiting concentrations were 1.56% v/v (HS-W) and 3.13% v/v (HS-W-CGO, HS-W-CG) at 24 h. These findings demonstrate that acidic matrices generate false-positive signals in standard enzyme-based screening. pH-matched buffer controls should be mandatory, and hsTYR is recommended over mushroom-derived surrogates for translational relevance.

Background and objective: A huge part of cosmetics research is devoted to the identification of new molecules and new ingredients which could prevent skin aging. Crithmum maritimum has attracted interest in the cosmetic field because it has been used since antiquity in traditional medicine and is traditionally consumed in Mediterranean regions. However, data about demonstrated efficacy on living cells remain sparse. To better understand the potential of this plant for the cosmetics industry, we aimed to investigate in vitro some key properties in line with anti-aging skin care. Methods and results: Molecular results demonstrated an impressive antioxidant effect which was confirmed in vitro on living keratinocytes with a decrease of 50% of oxidative stress measured with the fluorescent CM-H₂DCFDA probe. Additionally, an inhibitory effect around 20% was observed on isolated collagenase and elastase, highlighting the ability of C. maritimum to preserve the skin matrix. Lastly, anti-inflammatory properties were explored at protein levels by ELISA method, indicating a clear decrease of six inflammatory mediators, IL-6, IL-8, IL-18, CXCL9, CXCL10, and CCL5, on stressed keratinocytes. These observed decreases span from 20% up to 75% in the case of the IL-18. Conclusions: All together, these results reveal how efficient C. maritimum extract could be to alleviate signs of aging.