Essentail oils are often only active against certain classes of micro-organisms!

But we can use mixture to achieve large spectrum

Usually I used lotion/cream formula to test efficacy of essential oil as preservatives in cosmetic.

There is no standard formulation for testing efficacy of preservatives. The efficacy depends on lots of parameters (pH, adsorbants, chelators, ions ...).

The best is to perform challenge tests on several formulations (shampoo, cream such as cold cream, balm, ...).

Don't forget, also, to perform in vitro tests such as irritation assays, and tests on volunteers (patch tests ...)

And always keep in mind that if you are using essential oils, lots of them contain allergens, and irritant/cytotoxic molecules such as terpenes and their oxydized derivatives

Most cosmetics when tested are full of micro-organisms anyway. I hope you are not assuming the cosmetic formulations you test on will be sterile?

Cosmetics are supposed to be free of any contamination, otherwise 1/ they will not satisfy the legal rules and international standards, 2/ it will not be possible to perform some assays such as challenge tests. Additionallly, if there are microorganisms in your formulation in the prensence of your supposed preservative, this means the preservative is not efficient In summary, if there are microorganisms inside you formulation, through it away !

The plain fact is that commercially offered cosmetics are not sterile products and microbrial loadings can be quite high. Essential oils are poor preservatives in the sorts of concentrations allowed by the regulations. Sensitisation to EO's affects from 1 - 3% of the population but since most people who show allergic reactions tend to avoid products giving them problems, the actual incidence of sensitisation is probably therefore a lot lower.

Many scientists feel that the existing EU Health & Safety regs concerning sensitisation/irritation and other factors are too heavily based on data from research bodies such as IFRA whose continued existence depends on negative findings such as those reported for EO's.

Hi, there is no clear guidance on the carrier for any preservatives when evaluating, typically the best approach is to set up a small study using very basic parameters, such as an MIC (Minimum inhibitory concentration), using different solvents (with relevant +/- controls) you will be able to see which basic solvent will give the best efficacy. Use this to build up the next step, should the formulation be o/o, o/w water etc. The next steps that can be of use with EO formulation is investigate pH, and detergents to aid solubility. As I say there is no simple answer, rather you will need to investigate the formulation from the ground up that best supports the efficacy of your EO. One final point EO can differ greatly in shelf life, so as you are doing your initial studies these will be on 'fresh' samples, if you go to full formulation, you might lose efficacy over time, just be aware of that. and good luck.

Thanks to JC SERGERE, Gail Martin, Hartati Soetjipto and Kendra Kirkham. So, can you give me some exemples about cosmetic formulations (shampoo, cream ...).

Not sure what you are after specifically, you can't take a formulation and just 'add-in' a chemical and test for preservation. Take your active, and build a formulation around it. It will very much depend on what formulation suits you EO. For example, if your EO only works in oil based formulations, it might not work as well in shampoos, soaps etc (this is a very simplified view of course), therefore you might use your EO in a cream, lotion instead. You will need to do some basic studies on the solubility profile to understand where you could test. Remember the more complex the formulation you start with, the less likely you are to know where your preservation activity is coming from, start simple, and build round your EO.

Frankly the essential oils not act as preservatives ,if you need to creat natural formula you should add also natural preservative like grapefruit seed extract beside some kinds of essentail oils , some essentail oils act as antibacteria , and antifungal like tea tree....etc

Essential oils are normally used as saponification or emulsification agents but not as preservatives.Even formulations having oils with antimicrobial activity , other chemical preservatives like PPS/MPS/Benzoates etc are used to prevent degradation

If you are looking for basic formulas for shampoos or hand cream or liquid hand soap try the C&T(Cosmetic &Toiletries) magazine. However, I agree with all the comments above that EOs alone would not be very suitable as preservatives in cosmetic formulations due to many factors including concentration of the EO in the formulation, interaction with the surfactants, solubility, pH etc. Perhaps, you should look at synergies of the EOs with current preservatives used in cosmetic formulations as a way to reduce the amount of preservative needed . A preservative is added to cosmetic formulations to guard them from microbiological contamination during normal consumer use and their activity should last for the expected shelf life of the product. There are quite a few methods of preservative efficacy testing, for screening, I have used the the Cosmetic, Toiletry & Fragrance Association (CTFA) method.

As a basic formulation you can use a carbomer gel:

Glycerine 85%

15.00%

Carbopol ETD 2020

0.40%

Sodium hydroxide Sodium hydroxide solution, 15% aq.

0.90%

Aqua

ad. 100%

The formulation is published under:

https://www.researchgate.net/publication/232273504_Boosting_efficacy_of_preservatives

The advantage testing such gel is a minimised interference between the basic formulation and the preservative active, but especially water insoluble compounds might be difficult to be incorporated. Emulsion based products (w/o and o/w) are described in the enclosed paper:

KARIN M. STOFFELS, “Modern and safe antimicrobial stabilization of cosmetic products”, household and Personal Care today - n 1/2012

The microbiological tests should preferably be done according to ISO 11930, Cosmetics - Microbiology – Evaluation of the antimicrobial protection of a cosmetic product, or an other accepted challenge test for cosmetic products. An overview about test methods you can find under: https://www.researchgate.net/publication/232273427_ISO_11930__A_Comparison_to_other_Methods_to_Evaluate_the_Efficacy_of_Antimicrobial_Preservation

The determination of MIC values is only limited transferable to the efficacy as preservative in cosmetic formulations. The MIC is only a basic indicator for a certain antimicrobial effect.

Article Boosting efficacy of preservatives

Article ISO 11930 – A Comparison to other Methods to Evaluate the Ef...

Here is the paper with the emulsion formulations for cosmetic preservative testing

Thank you very much

You must use emulsions to test your preservatives preferably lipid emulsions