In this study, we investigated the chemical composition, antimicrobial and antibiofilm activities, and cytotoxicity of Thuja occidentalis L. (thuja) and Myrtus communis L. (myrtle) essential oils (EOs) to evaluate their potential as natural alternatives for topical applications. Thuja EOs were extracted from fresh and dried leaves and cones, while myrtle EO was extracted from fresh leaves. GC-MS analysis revealed that myrtle EO was rich in oxygenated monoterpenes (58.2%), predominantly eucalyptol (41.86%) and α-pinene (20.98%). In contrast, thuja EOs were dominated by monoterpene hydrocarbons (55–82%), with α-pinene as the major component (29–66%), and their composition varied markedly with plant organ and moisture state. Myrtle EO displayed the most potent and broad-spectrum antimicrobial activity, with MIC values as low as 3.096 µL/mL against Staphylococcus aureus and Escherichia coli, and effectively inhibited microbial adherence. Thuja EOs showed selective activity, particularly against Gram-positive bacteria and Candida parapsilosis, with EOs extracted from fresh leaves and cones exhibiting the lowest MICs (1.95–7.8 µL/mL). All EOs did not show cytotoxicity to human keratinocytes at concentrations ≤125 µg/mL and, when diluted to 0.05%, indicated excellent skin compatibility in human patch tests. This study suggests that myrtle and thuja EOs, particularly myrtle, are promising and safe natural antimicrobial agents for dermatological and cosmetic formulations.

Collagen is one of the main constituents of cosmetic formulations because of its moisturizing, regenerating, and film-forming properties. The aim of the present study was to obtain biocompatible collagen hydrolysates from Hypophthalmichthys molitrix skin, using a neutral inexpensive hydrolysis process involving low temperature (135 °C) and pressure values (315 kPa) and by using various pretreatment procedures (in order to eliminate the scales, fat, and meat). Comprehensive characterization of the hydrolysate samples confirmed their high purity, evidenced by a protein content exceeding 10%, undetected ash levels, and a pH between 6 and 7. This was further supported by optical microscopy and SEM imaging, which revealed the characteristic fibril structure. Additionally, FTIR analysis and CD spectroscopy verified a specific random coil structure and the complete absence of the triple helix characteristic of denatured collagen. EDX results confirmed the presence of C, O, N, and traces of S in all collagen hydrolysate samples. The results of the microbiological analysis for E. coli and S. aureus show either the complete absence or negligible amounts of fungi and bacteria in all hydrolysate samples, thereby demonstrating the effectiveness of the extraction process. The in vitro biocompatibility assessment established a non-cytotoxic concentration range between 1.25 mg/mL and 10 mg/mL for the tested samples, with cell viability above 70% and LDH release below 5%. Furthermore, clinical patch tests of the obtained fish collagen hydrolysates revealed no irritation reactions. Neutral hydrolysis of silver carp skin collagen hydrolysates with determined characteristics and favorable biocompatibility proves to be suitable for cosmetic applications.