Evaluation of the efficacy of lavender formulations as preservative agents in O/W (oil-in-water) emulsions

Use of preservatives in cosmetic formulations is an integral part of the manufacturing process, with the primary objective of eliminating or limiting the growth of microorganisms. Essential oils have emerged as a promising option, due to their antimicrobial properties and their ability to contribute to the microbiological stability of cosmetic formulations. To investigate and compare of the ability of lavender hydrosol and lavender essential oil to inhibit microbial growth and preserve the integrity of model cosmetic formulations over their expected shelf life. Lavender essential oil and hydrosol of the species Lavandula angustifolia, Mill were microbiologically evaluated. The sample containing both L. angustifolia hydrosol and essential, oil demonstrated the best overall performance. Addition of the essential oil seems to significantly enhance antimicrobial activity, compared to the hydrosol alone, decreasing the population of E. coli (Escherichia coli ) from an initial concentration of 9.8 ×10⁶ CFU (Colony Forming Units) / mL to 10 CFU/mL, whereas Pseudomonas aeruginosa decreased from 3.4 ×10⁵ CFU/mL to fewer than 10 CFU/mL. Staphylococcus aureus decreased from 6.9 ×10⁶ CFU/mL, to fewer than 10 CFU/mL, while the Candida albicans population exhibited a remarkable reduction from 2.0 ×10⁶ CFU/mL to 10 CFU/mL. The combination of hydrosol and essential oil resulted in significantly superior antimicrobial efficacy, suggesting a rather possible additional synergistic effect, compared to the hydrosol alone, surpassing the criteria B set by the European Pharmacopoeia.