With increasingly stringent preservative regulations matched with growing consumer demand for non-traditional preservatives, formulators have increasingly fewer options to protect personal care products from microbial attack.
Particularly difficult-to-protect formulations, like sunscreens, hair gels and wet wipes, pose challenges for formulators requiring broad-spectrum protection against bacteria, yeast and mould. In line with the trend to work with globally-approved preservatives, MIT (methylisothiazolinone) is increasingly considered an important component of preservative system solutions offering broad-spectrum protection. An MIT-based preservative with a booster ingredient, phenylpropanol, addresses a range of regulatory, consumer and formulator requirements. This article describes how Optiphen MIT Ultra may be used to solve preservation challenges globally and outlines preservative system efficacy in two difficult-to-protect personal care formulations, leave-on hair styling paste and rinse-off shower gel.
MIT-based preservative with nature-identical booster
Optiphen MIT Ultra (now referred to as ‘the MIT-based preservative’) is a patentpending liquid preservative blend of MIT with a booster that can be found naturally in flowers and fruits, such as strawberries, bilberries and blackberries. The booster component serves to broaden the activity profile of MIT against bacteria, yeast and mold. Historically, formulators have relied tremendously on formaldehyde-donors or halogen based chemistry when faced with challenging formulations. However, with consumer demand for non-traditional preservatives and increasing scrutiny by regulators, the formulator is challenged to fulfill both obligations. New MIT-based blends offering broad-spectrum protection must simultaneously accommodate tighter regulations and consumer perceptions. Further limiting the choices of formulators today is the fact that some conventional preservative blends may be deactivated in neutral and alkaline conditions or at temperatures above 40°C. Broad-spectrum preservatives must withstand wide pH ranges, elevated temperatures and the presence of nucleophilic reactive ingredients. In addition, they should be cost-effective. The MIT-based preservative achieves all of these requirements with a single preservative active ingredient labelled as methylisothiazolinone. Based on MIT and phenylpropanol, the new MIT-based preservative protects against bacteria, yeast and mould in leave-on and rinse-off applications at usage levels of 0.05% to 0.3%. The nature-identical booster included in the system works by broadening the efficiency against yeast and mould. The product is compatible with a wide range of commonly used personal care ingredients. The colourless to yellowish solution does not affect the rheology or colour of finished formulations. Figure 1 shows the molecular structure of the components.
Performance profile
MIT, approved for use in technical product formulations for many years, already has an established track record of performance and is now approved globally as a preservative for personal care products. Table 1 lists the major functional benefits of the MIT-based preservative in personal care formulations.
Preservative system efficacy
Challenge tests / repetitive inoculations verify the effectiveness of the MIT-based preservative in personal care formulations. Researchers tested a moldable hair paste and shower gel – two difficult-to-protect formulations – to demonstrate broadspectrum efficacy against a wide range of microbes. Following a 28-day double challenge test method, the products are inoculated at the onset of testing (0 hours) and then assayed at 48 hours and seven-day intervals. At 21 days, the formulations are re-inoculated with the same microorganisms. Pass/fail criteria are based on kill rate following inoculation. Challenge test results show the MIT-based preservative provides broadspectrum preservation in a rinse-off formulation.
Summary of preservative efficacy
The MIT-based preservative is proven to protect a variety of personal care formulations against micro-organisms efficiently and effectively. Twenty-eight-day challenge test results show that MIT based preservative system with a preservative booster – phenylpropanol – may be used to preserve formulations traditionally considered as difficult to preserve, such as styling products and body washes. Additional preservative efficacy test results not included here show sunscreens, lotions, creams, shampoos and conditioners are well-preserved by the MIT-based preservative.
Conclusion
Personal care product formulators have better options to protect formulations from microbial attack with MIT based preservatives designed for broadspectrum protection. Optiphen MIT Ultra, containing a nature-identical booster found naturally in some flowers and fruit, functions as a very efficient preservative system serving as an alternative to parabens, formaldehyde- donors and halogen-based chemistry. Very effective at low dosage rates, Optiphen MIT Ultra is ideal for difficult-to-protect personal care formulations. Based on preservative efficacy test results, Optiphen MIT Ultra is recommended for use between 0.05%-0.2% in rinse-off applications and between 0.1%-0.3% in leave-on formulations. PPCC
Acknowledgement The authors would like to thank the ISP microbiological department led by Susan Lindstrom, for conducting the preservative efficacy testing and Jose Santiago-Martinez for formulation work at Wayne, NJ (USA).
