Tips to Select Preservative for Cosmetics

Several products in the market contain ingredients which make cosmetic systems very difficult to preserve. For example, personal care products contain significant amounts of water and other ingredients that may be susceptible to contamination by microorganisms like bacteria, fungi, and molds.

In order to prevent such happenings, formulators include preservatives in their formulations. Preservatives protect the integrity and stability of cosmetic products that can be damaged by microorganisms.

While applying a cosmetic for personal care use it should be assured that it is free from any contamination. The product must be preserved adequately to kill the microorganisms that are introduced by the consumers themselves. However, one also must be careful with over-preserving a product as too much preservative in a product is not good either.

Preservative Chemistries

Preservatives by their chemistry can fall under two categories: Natural & Synthetic.

Natural preservatives are extensively used while formulating natural cosmetic products. Most formulators are only aware of the most common natural preservatives but there is a whole family of ingredients which can work quite well in killing microorganisms. Of late, the effectiveness of essential oils in killing bacteria has been examined by many people in the cosmetics industry.

On the other hand, synthetic preservatives are specifically designed molecules that work as broad-spectrum antimicrobials. Some common types of preservatives used in cosmetic formulations with their features are listed in the table below.

Preservative Type	Features	Examples
Organic acids	Need to be added in higher quantities for optimum preservation, thus costly Effective with fungi but offer least protection against bacteria Need an aqueous base, in order to be used Considered natural alternatives while developed synthetically Offer a broad spectrum of effectiveness when combined with other organic acids or diazolidinyl urea (DU)	Benzoic acids and salts Sorbic acid and derivatives Formic acid and derivatives...
Parabens	Mostly used preservatives with cosmetics (both rinse-off and leave-on) Unlike organic acids, these are cost-effective Rendered inactive in combination with polysorbate emulsifiers Good protection against fungal growth and gram positive bacteria Can be used at levels ranging from 0.01 to 0.3%1 Considered carcinogenic	Methylparben Propylparaben Butylparaben...
Urea Compounds/ Formaldehyde releasing preservatives	Effective in fighting bacteria but weak fungal efficacy Low levels required for use as these release formaldehyde needed for preservation Can cause skin irritation / allergic reactions Used in skincare and toiletries	DMDM Hydantoin Imadozolidinyl Urea Diazolidinyl Urea

As a formulator, one must do ample research to find the right combination of preservatives to kill any contaminants that may find their way into cosmetic products. More research is required simply because many preservatives that worked very well in the past are not being used any longer by the formulator. While speaking of it looks easy, formulating with preservatives can sometimes be very difficult.

Criteria to Select the Right Preservative

The selection of a preservative for a formulation is undoubtedly one of the most important, yet most controversial aspect a formulator has to see. With so much of choice in preservatives available, and so much misinformation on the internet, how does a formulator make the Perfect Preservative Selection?

There is no single preservative that will suit all formulation types and company/product philosophies or product types. Technically, any preservative that is used within limits as specified by regulators in a particular region, and where suited to the product type and end consumer, is suitable for selection.

Despite popular (yet misinformed) reports on the internet, preservatives when used within limits specified by the regulators are considered ‘safe’ and suitable for use. So just how does a formulator make the best, if not the ‘Perfect’, preservative selection? There are some key elements that need to be considered, which we’ll now explore…

Company/ Product Philosophy

The first selection step a formulator needs to make is based on the company and/or product philosophies, particularly if there are claims being made about ‘natural’, or ‘avoiding’ the use of certain ingredients and/or if Organic certification (or other certification, for that matter), is required.

If a company specifically requests the ‘avoidance’ of certain materials, then preservatives containing those materials must be specifically avoided. If a company is after certification, then only preservatives that comply with the Certifier’s requirements may be selected. As a first step in preservative selection, company/product philosophy and the specific use or avoidance of certain ingredients obviously narrows the choice of preservatives that can be used depending on the selection criteria specified.

Also, part of the company/product philosophy considerations is:

• On whom will be the finished product used? For example, babies vs. children vs. adults.
• What part of the body will it be used on? For example, mucous membranes vs. around the eyes vs. external skin of the legs.
• Will the product be washed off or left on; and how often will it be applied? For example wash off products with relatively short contact time vs. regular-use products that are to be left on the skin.
• Does the preservative carry an aroma that may (or may not) be suited to your target market and product requirements?

Regulatory Considerations

To be used in a personal care product, preservatives must be permitted in the countries in which the product will be sold, and be used within any limits or conditions of use specified. For example, most preservatives have very specific ‘limits’ on addition, and can only be used within the limits specified.

Other preservatives may have very specific conditions of use, for example, in wash off products only, or not on mucous membranes. In such cases, conditions of use must be adhered to, to ensure regulatory compliance of the finished product.

Limits and conditions of use imposed by regulators have generally been set based on evaluations of safety; so using preservatives in compliance with the regulations is not only a legal requirement but also an important safety consideration to ensure ‘safety when used as directed’ of a finished product.

Product Form

The form of the product will be the next biggest selection criteria, which can impact on preservative selection based on:

• Finished product transparency required (or in the case of emulsions, this may not be important at all!)
• Dispersibility/solubility of the preservative: ensuring a preservative can be easily and homogeneously distributed is crucial to ensure a product is adequately preserved in all areas of a large vat!
• Chemical nature of the product: some preservatives are particularly not suited to charged (anionic or cationic) environments while others may work better in these mediums
• Free water content and Microbial Risk Classification (MRC) of materials used in the formulation: materials with higher risk ingredients will need stronger acting preservatives; this does not mean one should ‘over-preserve’ a product, but that careful selection needs to be made to ensure broad spectrum coverage and synergy of blends used to ensure adequate microbial protection of the finished product

pH

Finally, and just as importantly, the pH of the finished product is essential to be considered. This includes not just the pH of the finished product when it is manufactured, but must also allow for pH drift over the shelf life of the product. The pH of a product containing water will move over its shelf life. It is quite typical for the pH of a finished product to move +/- 10% over its shelf life; sometimes this drift can be up to +/- 20%!

Selecting a preservative with a limited pH range of compatibility could leave your product un-preserved should a large pH drift occur – so when selecting your preservative, make sure you consider a potential pH drift of at least +/-10%, if not a little more, to ensure adequate efficacy of the preservative over the shelf life of the product.

How do you put this together to make the Perfect Preservative Selection?

To help make sure you make the right preservative selection, use the selection steps above and then double check your selection using the checklist.

Does the preservative provide broad spectrum coverage?

• Even if the product is at a low or high pH and therefore unlikely to grow certain types of micro-organisms based on the environment, some micro-organisms can still grow outside of their normal pH range.
• It is therefore essential that you select a preservative system providing broad spectrum coverage in all cases where product contains a high free water content.

Does the preservative suit the organizational product philosophy?

• It is essential to make sure that your preservative suits the organizational philosophy otherwise it will not comply with the development requirements. Where there are conflicts with the required preservative and organizational philosophy, you will need to discuss this with the concept developer for further guidance.

Does the preservative suit the pH of the finished product?

• Make sure you allow for pH drift which is a natural process over the shelf life of the product.
• Generally speaking, you should make sure that your preservative selection allows for at least a 10% pH drift (up or down) over the shelf life of the product. For example, if your finished product is pH adjusted to 5.0, then the preservative you select should provide effective coverage to at least 4.5 - 5.5 to ensure it provides suitable coverage over the normal pH variances that occur throughout the shelf life of the product.

Does the preservative have incompatibilities with any ingredients?

• If it does, it could be rendered ineffective. Make sure to thoroughly investigate the preservative system you are intending to use to check for any incompatibilities and if these apply to the product you are formulating.

Has the preservative been added at the appropriate temperature/method etc.?

• Make sure you check how the preservative should be incorporated into your formulation, and ensure this is clearly stated in the formula by including it in the correct phase as well as written into the method below the formula.


• Preservatives should be added to the water phase as early as possible during processing, but this is obviously not appropriate where they are not water soluble, not suitable to be heated (if the product needs to be heated) or where the pH is not suitable – you don’t want to de-active your preservative by not following its required processing instructions!
  
  If the pH or temperature is not going to be suitable for your preservative early in the processing method, then add it at the end when the temperature is appropriate, and just before pH adjustment at the final stage of processing.


• Make sure that the form of the preservative suits the form of the finished product, or can be incorporated easily, to ensure homogeneous distribution. Use a slurry method to disperse powders or add preservatives in liquid form to enhance a more homogeneous distribution.


• If the product is intended to be clear, make sure you have selected a preservative that will appear clear in the finished product.

Preservatives Product Range

View a wide range of preservative grades available in the market today, analyze technical data of each product, get technical assistance or request samples.