One of the most common type of questions we get asked here on Chemists Corner is about natural preservatives. On the one hand this is great because it demonstrates that people understand they should be using preservatives when formulating cosmetics. On the other hand it is troubling that some formulators (or the marketing people they answer to) have lost faith in standard, proven effective & safe, preservatives.
But there is certainly a desire to have formulation preservative strategies that stay away from using traditional preservatives such as parabens, formaldehyde donors, and organic biocides. We’ll look at some natural preservation options below.
Hurdle strategy of cosmetic preservation
In the old days of formulating if you had a microbial problem you could simply put in parabens and formaldehyde donor ingredients and that would be effective most of the time. If you had a particularly persistent problem you could also include something like Kathon. As a natural formulator those ingredients are generally frowned on and not allowed. This means you’ll need some alternative cosmetic preservatives. But even before choosing a new preservative you can employ hurdle strategy for reducing the preservative need.
Hurdle technology - The idea behind hurdle technology comes from the food industry. This strategy involves finding different materials and factors that inhibit microbial growth on their own but at high levels. By combining these factors you can reduce the amount of any of them while still killing off more and more microbes. The idea is that you make it more and more difficult for microbes to grow and thus have a preserved product. Some of the factors involved in hurdle technology include
- Low pH - Most bacteria grow best at a pH level of 6.5 - 7.0. Fungi grow better at pH levels from 5.0 - 6.0. So, if you keep your pH below 5.0 you help preserve your products.
- Heat - Use of heat during production can reduce the initial microbial count and help preserve your product.
- Reduce water - If you use a lower level of water activity or include ingredients that can tie up water in your system microbes can’t grow. With a water activity level below 0.87 most organisms won’t grow.
- Anhydrous - of course you could just make an anhydrous formula. This limits your options but it also reduces the amount of preservative you need.
- Chelating agents - These ingredients can help boost the effect of your preservative. Standard cosmetics would use EDTA but for natural formulators you can try an ingredient like phytic acid extracted from rice bran.
- Antioxidants - These will help prevent rancidity and will also slightly inhibit microbial growth. Antioxidants are more relevant in food products than cosmetics.
- Emulsion type - Products that are Water-in-Oil emulsions require less preservatives than the typical oil-in-water emulsion. This is because it is more difficult for microbial colonies to establish themselves.
- Packaging - You can use single use or air tight packaging which will make it difficult for microbes to grow. This would reduce your need for a preservative.
While hurdle technology will help, it is not usually enough to preserve your products. You still need a preservative. If you don’t want to use standard products here are some options.
Phenoxyethanol - This ingredient is not approved by COSMOS but it is a common preservative for natural formulators. It is a solvent for fragrances and has a light rose odor. It is effective against some bacteria and fungi. Also good against pseudomonas. It has a wide pH range and is effective from pH 3 - 10.
Phenethyl Alcohol - This ingredient is approved by COSMOS and works similarly to phenoxyethanol. It has a stronger odor however.
Organic acids and their salts - There are a wide range of organic acids that are effective as preservatives. These include
- Benzoic acid
- Sodium benzoate
- Sorbic acid
- Potassium Sorbate
- Dehydroacetic Acid
- Salicylic acid
These ingredients are mostly approved by the COSMOS standard and are effective against fungi and to some extent bacteria. They only work at lower pH however so if you use them you need to formulate below pH 5.0
Benzyl Alcohol - This material is effective against a broad spectrum of microbes. While it can be found in nature most of the benzyl alcohol used commercially is synthetically produced. One drawback is that it is a known allergen. There are also some compatibility issues with benzyl alcohol and nonionic surfactants.
Natural preservative boosters
Less effective ingredients that can help boost the efficacy of alternative preservatives include
The following ingredients can help disrupt growth by interfering with the microbial cell membranes.
- Caprylyl Alcohol
- Caprylic Acid
- Glyceryl Caprylate
Other fragrance components have some preservative boosting activity
- Levulinic Acid
- p-Anisic Acid
There are also some enzymatic systems that have been successfully employed in natural cosmetic formulations.
- Glucose Oxidase
Finally, there are some natural ingredients that have some antimicrobial functionality. They are not broad spectrum effective so should not be used as the sole preservative system.
- Tea tree oil
- Aspen bark extract
- Grapefruit seed extract
- Honeysuckle extract
If you are formulating natural cosmetics and need a preservative system, your best strategy would be to use some of the suggestions above. Admittedly, preserving products using only natural ingredients is difficult. Be sure to test everything you make multiple times until you are certain your preservative system will be adequate. And as always, make the products in as clean an environment as possible.