Article by: Guest Author

This is a guest post by Rachelle Baker, lab manager at Cosmetic Test Labs.

A popular trend in the cosmetic and personal care product industry is to “go green.” For most manufacturers, the switch to all-natural ingredients stems from a desire to improve the environmental fate, enhance safety, and improve marketability of their products. Makers and formulators of cosmetics can benefit from reading this article, which lays out the case for preservative challenge testing, even when a formula contains a well-known preservative ingredient.

Product Testing

Most manufacturers know that using natural or new ingredients not commonly used in the market can negatively affect product stability. For that reason, they often carry out physical stability tests, chemical stability tests, and microbial challenge studies. These studies give them faith that their products will look, smell, and perform just as well when purchased as after production.

Unreliable preservation

What many product formulators don’t know is that you can’t always depend on well-known preservatives to keep a product safe and stable. For example, paraben and hydantoin-based preservatives have been around for many years and are functional in countless products. Is it still necessary to test them in your firm’s formulation? The answer to this question is yes, as explained further, below.

Top reasons why all basic formulations should undergo preservative challenge testing:

Preservative activity

The activity of a preservative depends on the combination of all the product ingredients and the packaging used. As ingredients are mixed together to create a formula, chemical changes can occur that decrease the efficacy of the antimicrobial agent. For example, an anionic (negatively charged) detergent might bind to a cationic (positively charged) quaternary ammonium preservative, preventing it from interacting with microorganisms. Therefore, preservative efficacy of a product cannot be predicted based on its individual ingredients alone. It must be established through microbial challenge testing of the complete formulation.

Product pH

The pH of a formula is closely tied to the potency of its preservative package. As the literature of many manufacturers shows, preservatives have optimal pH ranges. Elevated or decreased pH may render preservatives useless.

Better against some than others

Most presevatives do better against some types of microorganisms than others. For example, parabens mostly protect against gram-positive bacteria. Thus, a cosmetic formulator may need to employ a mixture of preservatives to protect against different bacterial strains as well as yeasts and molds. Since each individual preservative will likely be used at levels at or below manufacturer recommendation to make the custom blend, the final product’s resistance to microorganisms will need to be verified as effective for the complete formulation.

Legal responsibility

According to the FDA, companies and individuals who market cosmetics have the legal responsibility to ensure the safety of their products. FDA may even buy cosmetics and analyze them. So even if a formula is a knock off of another formula that you know has been tested for safety, it is still the responsibility of the individual marketing the product to ensure the safety of that product and need to be prepared if the FDA comes knocking. If for no other reason, manufacturers can undertake preservative challenge testing to verify that their products are free from microorganisms should they be analyzed by FDA.

Preservative efficacy testing is important to ensure the safety of cosmetic and personal care products. It remains the responsibility of the finished product manufacturer to substantiate the safety of both ingredients and finished cosmetic products prior to marketing.

Preservative compatibility

It is important to determine if the preservative chosen for a product is compatible with the formulation soon after manufacture. It is also a good idea to test again within 2-3 months of manufacture or as appropriate to the intended shelf-life as part of your stability testing regimen. It will be necessary to re-evaluate preservative effectiveness in your product whenever a formulation, or manufacturing process has been changed or when product packaging changes occur.


  1. Avatar

    what are the best preservatives are best with gram negative and positive microbe coverage,that can be mixed together, and also best for mold and fungus

  2. Avatar

    What would be a good company to send formulas off for testing? I need to send 2 new formulas off to determine shelf life etc

    1. Avatar
      Perry Romanowski

      You can try

    1. Avatar
      Perry Romanowski

      Well, I’d suggest sending out your products to get independent testing. When you test it yourself you open yourself up to claims of faking the data.

  3. Avatar

    “The pH of a formula is closely tied to the potency of its preservative package. As the literature of many manufacturers shows, preservatives have optimal pH ranges. Elevated or decreased pH may render preservatives useless. What do you mean by this?

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