Preservatives are added to cosmetics to protect the consumers from infections and prevent product spoilage. The concentration of preservatives should be kept as low as possible and this can be achieve ...

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Preservatives are added to cosmetics to protect the consumers from infections and prevent product spoilage. The concentration of preservatives should be kept as low as possible and this can be achieved by adding potentiating agents. The aim of the study was to investigate the mechanisms behind potentiation of the bactericidal effect of a commonly used preservative, 2-phenoxyethanol (PE), by the potentiating agent ethylhexylglycerin (EHG). Sub-lethal concentrations of EHG (0.075%) and PE (0.675%) in combination led to rapid killing of E. coli (> 5 log reduction of cfu after 30 min), leakage of cellular constituents, disruption of the energy metabolism, morphological deformities of cells and condensation of DNA. Used alone, EHG disrupted the membrane integrity even at low concentrations. In conclusion, sub-lethal concentrations of EHG potentiate the effect of PE through damage of the cell membrane integrity. Thus, adding EHG to PE in a 1:9 ratio has a similar effect on membrane damage and bacterial viability as doubling the concentration of PE. This study provides insight about the mechanism of action of a strong potentiating agent, EHG, which is commonly used in cosmetics together with PE. (1)

The synergistic performance of caprylyl glycol, phenethyl alcohol and glyceryl caprylate and the anti-microbial activity of their blend suggest that their combination is effective and exhibits broad-spectrum anti-microbial activity. Furthermore, the results show a positive correlation between the anti-microbial activity of the preservative and the particle size of the emulsion droplets in the range of 100-900 nm, when the same concentration of the blend is used in the same formulation. The particle size of the emulsion droplets is demonstrated to be a newly discovered factor that influences the preservation of cosmetic products (2).

Caprylyl glycol and related 1,2-glycols are used mostly as skin and hair conditioning agents and viscosity agents in cosmetic products, and caprylyl glycol and pentylene glycol also function as cosmetic preservatives. The Cosmetic Ingredient Review (CIR) Expert Panel noted that, while these ingredients are dermally absorbed, modeling data predicted decreased skin penetration of longer chain 1,2-glycols. Because the negative oral toxicity data on shorter chain 1,2-glycols and genotoxicity data support the safety of the 1,2-glycols reviewed in this safety assessment, the Panel concluded that these ingredients are safe in the present practices of use and concentration described in this safety assessment (3).

Nanosuspensions as aqueous formulations need to be preserved. However, preservatives could vitiate the physical stability of suspensions and to a greater extent nanosuspensions. The impact of six varied preservatives on the physical stability of previously prepared nanosuspensions was studied. The hesperetin nanosuspensions were stabilized using plantacare 2000.30 cycles of high pressure homogenization (HPH) led to a mean photon correlation spectroscopy (PCS) diameter of 335 nm. The preservatives were, caprylyl glycol, Euxyl PE9010, Hydrolite-5, MultiEx naturotics, Phenonip and Rokonsal PB5. On one hand, aggregations were noticed after adding caprylyl glycol, MultiEx naturotics and Phenonip reaching PCS mean diameters of about 500, 1070, 800 nm, respectively. While on the other hand Euxyl PE9010, Hydrolite-5 and Rokonsal PB5 have not significantly affected the physical stability of the nanosuspensions with mean PCS diameters of about 365, 332, 350 nm, respectively. The obtained nanosuspensions were further characterized by measuring zeta potential. From the obtained data it was found that the lipophilicity of the used preservatives demonstrates major influence on the stability of the nanosuspensions, i.e. the higher lipophilicity of the preservative, the stronger the destabilizing effect. Briefly, highly hydrophilic preservatives are recommended to preserve hesperetin nanosuspensions in order to maintain their physical stability during storage (4).

Other studies

Contact urticaria following the use of a cosmetic containing caprylyl glycol: A case report.
Coelho EQ, Wu SLC, Nunes RS, Reis VMS.
Contact Dermatitis. 2019 Apr 26. doi: 10.1111/cod.13299.

Determination of alternative preservatives in cosmetic products by chromophoric derivatization followed by vortex-assisted liquid-liquid semimicroextraction and liquid chromatography.
Miralles P, Vrouvaki I, Chisvert A, Salvador A.
Talanta. 2016 Jul 1;154:1-6. doi: 10.1016/j.talanta.2016.03.033.

A new alternative to cosmetics preservation and the effect of the particle size of the emulsion droplets on preservation efficacy.
Fang B, Yu M, Zhang W, Wang F.
Int J Cosmet Sci. 2016 Oct;38(5):496-503. doi: 10.1111/ics.12317.

References____________________________________

(1)  Ethylhexylglycerin Impairs Membrane Integrity and Enhances the Lethal Effect of Phenoxyethanol  Solveig Langsrud, Katrin Steinhauer, Sonja Lüthje, Klaus Weber, Peter Goroncy-Bermes, Askild L. Holck  PLoS One. 2016 Oct 26;11(10):e0165228. doi: 10.1371/journal.pone.0165228.

(2) A new alternative to cosmetics preservation and the effect of the particle size of the emulsion droplets on preservation efficacy.
Fang B, Yu M, Zhang W, Wang F.
Int J Cosmet Sci. 2016 Oct;38(5):496-503. doi: 10.1111/ics.12317.

(3) Safety assessment of 1,2-glycols as used in cosmetics.
Johnson W Jr, Bergfeld WF, Belsito DV, Hill RA, Klaassen CD, Liebler D, Marks JG Jr, Shank RC, Slaga TJ, Snyder PW, Andersen FA.
Int J Toxicol. 2012 Sep-Oct;31(5 Suppl):147S-68S. doi: 10.1177/1091581812460409.

(4) Preserving hesperetin nanosuspensions for dermal application.
Al Shaal L, Müller RH, Keck CM.
Pharmazie. 2010 Feb;65(2):86-92.

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