Aims:  The aim of the study was to verify the antimicrobial activity of commercial essential oils: lavender, tea tree and lemon as the components of a preservative system in oil in water body milks. Methods and Results:  The inhibition efficacy of essential oils alone (0·5%), in mixtures (1%) as well as combined with the synthetic preservative 1,3‐dimethylol‐5,5‐dimethylhydantoin and a 3‐iodo‐2‐propynyl butyl carbamate mixture (0·1% and 0·2%) was tested against Staphylococcus aureus ATCC 6538, Pseudomonas aeruginosa ATCC 9027, Candida sp. ŁOCK 0008 and Aspergillus niger ATCC 16404 in compliance with the standards of the European Pharmacopoeia Commission. The in vitro activity of oils determined by an impedimetric method was also compared with their activity in cosmetic preparations. Criterion A for bacteria (reduction in the inoculum by 3 logarithmic units within 7 days with no increase up to the 28th day) and fungi (reduction in the inoculum by 2 logarithmic units within 14 days with no increase up to the 28th day) was fulfilled for cosmetic formulations containing the tested essential oils with 0·2% of the synthetic preservative. The preservative concentration could be decreased to 0·1% (with preserving the same efficacy) in combination with lavender and tea tree oils at a concentration of 0·5% each. Conclusions:  In all combinations of essential oils with the synthetic preservative, a synergistic effect of the preservative system components was observed, which made it possible to reduce the usable level of the synthetic preservative up to 8·5 times. Significance and Impact of the Study:  To develop an effective preservative system in cosmetics in which a synthetic chemical preservative is replaced by natural essential oils.

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Pyrazole exhibits exceptional effects of temperature and pressure for H-disorder in hydrogen bonds NH···N. Under normal conditions, α-pyrazole is polar (orthorhombic space group Pna21), but the structure is pseudo-centrosymmetric. Two symmetry-independent molecules differently favor the H-sites at their amine nitrogen atoms. The asymmetric disorder of protons in hydrogen bonds NH···N leads to the disproportionation favoring the cations at one site and anions at the other. High temperature increases distortions of the structure from the centrosymmetric symmetry, activates the disproportionation defects, and stabilizes the averaged ionic disparity of symmetry-independent molecules at the ±0.1 e̅ level. Critical pressure P c = 0.45 GPa induces a transition to centrosymmetric phase β, space group Pnab. This transition involves the 50:50 H-disordering in NH···N hydrogen bonds and eliminates molecular displacements as well as the favored H-sites. The NH···N bonds are hardly compressed at P c in pyrazole, and they are by over 0.4 Å longer than the OH···O– bond in KH2PO4 (KDP). The main structural transformations are reorientations of pyrazole molecules, which suggests the primarily displacive character of this pressure-induced phase transition.

The aim of this study was to evaluate the antimicrobial activity of commercial essential oils: lavender, tea tree and lemon, antimicrobials in washing liquid and O/W soft body balm. The inhibition efficacy of essential oils in washing liquid (1% alone or in mixtures), in soft body balm (0.5% alone), as well as combined with the synthetic preservative DMDM hydantoin and 3-iodo-2-propynyl butyl carbamate mixture (0.1 and 0.3%), was tested against S. aureus ATCC 6538, P. aeruginosa ATCC 9027, Candida sp. ŁOCK 0008 and A. niger ATCC 16404 in compliance with the European Pharmacopoeia standards. The components of the system preserving soft body balm were supplemented with a solubilizer. Washing liquids containing only essential oils met Criterion A E.P. only for S. aureus, Candida sp. and A. niger. In soft body balm formulations, oils at a concentration of 0.5% did not reveal any preserving activity. The introduction of a solubilizer to a system containing 0.5% tea tree oil led to a substantial increase in the bacteriostatic activity of the formulation, but did not significantly affect its fungistatic properties. A combination of 0.5% tea tree oil, 5% solubilizer and 0.3% synthetic preservative ensured the microbiological stability of soft body balm in accordance with Criterion A E.P.