## 5 Conclusions  
The conducted studies revealed the significant potential of eugenol and isoeugenol as natural terpene compounds with antimicrobial properties, which could play a crucial role in the improvement of microbiological stability and the safety of cosmetic formulations. During the antimicrobial activity tests, both compounds showed high effectiveness in the elimination of microorganisms such as Gram-positive bacteria, including _Staphylococcus aureus_ and _Enterococcus faecalis_, as well as yeast-like fungi, including _Candida albicans_ and _Candida glabata_, which are the commonly occurring pathogens in cosmetics. The obtained results clearly indicate the possibility of using eugenol and isoeugenol in cosmetic products to prevent microbial growth, which is crucial for ensuring the quality and long-term stability of these products. Both eugenol and isoeugenol act in a similar manner by destabilizing the cell membranes of microorganisms and inhibiting the enzymes essential for their survival. This mechanism not only inhibits the growth and development of bacteria and fungi but also limits their ability to produce toxins and other virulence factors. As a result, eugenol and isoeugenol demonstrate versatility in combating microorganisms, showing antimicrobial activity at multiple levels, making them valuable ingredients in cosmetics. The primary advantage of applications of eugenol and isoeugenol in cosmetic formulations is their potential to replace the traditional, often synthetic preservatives, which in many cases can cause allergic reactions or skin irritation. Eugenol and isoeugenol show a favorable safety profile, especially regarding the skin, making them attractive alternatives to conventional preservatives in cosmetics. In a time of increasing demand for products based on natural ingredients, eugenol and isoeugenol can meet the needs of consumers looking for health-promoting products while also ensuring the safety of application. Although eugenol and isoeugenol exhibit promising antimicrobial properties, further research is necessary to determine their optimal concentrations in various cosmetic formulations. These studies should include not only the evaluation of these compounds' effectiveness in eliminating microorganisms but also their impact on the microbiological stability of cosmetic products over an extended period and under various storage conditions. Additionally, it is important to conduct comprehensive safety tests regarding their application in cosmetics, including toxicity studies and assessments of the potential interactions with the other cosmetic ingredients. These analyses will allow for the precise determination of the concentration limits of these compounds, ensuring their maximum effectiveness while minimizing the risk of undesirable reactions. In conclusion, the results of these studies highlight the significant potential of eugenol and isoeugenol as natural preservatives and antimicrobial substances, which could contribute to reducing the application of synthetic chemical compounds in the cosmetics industry. The application of these compounds in cosmetics can not only support the growing trend of natural products but also meet the needs of consumers seeking products that are effective, safe, and environmentally friendly. The application of eugenol and isoeugenol in cosmetics represents a promising path for the development of innovative, natural alternatives to traditional methods of preserving cosmetic products. Conceptualization. A.F.-B., J.P. and A.W. ; methodology. A.F.-B., J.P. and A.W. ; validation. A.F.-B., J.P. and A.W. ; formal analysis. A.F.-B., J.P., W.Z. and A.W. ; investigation. A.F.-B., J.P. and A.W. ; data curation. A.F.-B., J.P., W.Z. and A.W. ; writing--original draft preparation. A.F.-B., J.P. and A.W. ; writing--review and editing. A.F.-B., J.P. and A.W. ; visualization. A.F.-B., J.P., W.Z. and A.W. ; supervision. A.F.-B., J.P., A.W., A.L. and A.K. All authors have read and agreed to the published version of the manuscript.