Emulsifier system influences O/W emulsion preservation

This includes the necessity for an adequate preservation system in the cosmetic product to prevent microorganisms potentially endangering the consumer’s health from growing. The preservation of personal care products is achieved by the addition of antimicrobial ingredients. Their properties however bear the potential for undesired effects on the skin. In 1982 a positive list of approved preservatives was adopted as Annex VI to council directive 76/768/EEC,1 which later turned into Annex V of regulation EC 1223/2009. 

In addition to the approved preservatives listed on Annex V, a large number of other personal care ingredients exhibit inherent antimicrobial activity, which may be exploited to complement the overall preservation of a cosmetic product as a secondary function of the ingredients, such as chelators, wetting agents, fragrance ingredients, moisturisers, solvents, antioxidants and others.2 In fact, most personal care ingredients either have a positive or negative effect on the overall antimicrobial effect of a formulation. Only a few ingredients are inert in the sense that they have absolutely no influence on the preservation of a product. 

The nature of the influence of the ingredients on the antimicrobial performance can be manifold. Some ingredients have a negative effect on microorganisms by affecting the cell membrane or the cell metabolism after penetration into the cell, while others stimulate microbiological growth by the ability of the microorganisms to metabolise the ingredient. In addition, interaction between the ingredients may lead to inactivation of antimicrobial active components. Antimicrobial components with surface activity can be attracted by detergent micelle structures in rinse-off formulations or by emulsifiers in the interphase of emulsion systems. A variation of the polarity of the oil-phase has an influence on the partition of antimicrobial ingredients between the water-phase and the oil-phase.