Developing translucent emulsions using sustainable NADES-based extracts

In this work, we explored natural deep eutectic solvents (NADES) for developing translucent NADES-in-oil emulsions (TEs) for cosmetic applications. NADES, composed of lactic acid and glycerol (1:1 and 1:4 ratios), were selected for their natural origin, non-toxicity, and compatibility with living organisms. These green solvents facilitated the extraction of bioactive compounds from Lavandula angustifolia , Corymbia citriodora , Thymus vulgaris , Quercus suber , Allium sativum , and Origanum vulgare . The resulting NADES-extracts were characterized using LC-MS for compound identification and incorporated into TEs formulations. The content of phenolics, flavonoids, chelating power, and the antioxidant activity were assessed for both NADES-extracts an TEs. The produced TEs (50 wt% egg L-α-phosphatidylcholine (EPC), 20 wt% ethanol, 20 wt% olive oil, and 10 wt% NADES/NADES-extracts) effectively hindered the activity of enzymes responsible for skin melanin regulation and aging, namely tyrosinase (IC 50 ≈ 0.18 mg/mL for eucalyptus) and elastase (IC 50 ≈ 0.23 mg/mL for thyme). Gram-negative bacteria, particularly K. pneumoniae , were found to be more susceptible to NADES-extracts and TE-extracts, resulting in larger zones of inhibition. The study reported no toxic effects in the larval model, with a noticeable decrease (2-fold) in melanization in G. mellonella larvae after TE application. Cytotoxicity results indicated that TEs could be tolerated in skin cells at concentrations up to 5 %. Transdermal testing showed TEs permeation into the skin of 1–5 %, suggesting their use for cosmetic purposes without significant cellular damage. This study highlights the potential of NADES combined with natural extracts as sustainable, non-toxic ingredients in cosmetic formulations, paving the way for innovative skin regeneration products.