In the world of cosmetics, safety extends far beyond attractive packaging and innovative formulas. Behind every bottle of face cream or jar of body butter is a scientific process that ensures what you put on your skin is clean, stable, and safe. An essential part of this process is Preservative Efficacy Testing (PET)—also known as challenge testing. PET is not just a regulatory checkbox; it ensures your product remains free from harmful microbes throughout its shelf life, protecting both your customers and your brand.
What Is Preservative Efficacy Testing (PET)?
Preservative Efficacy Testing evaluates how well a cosmetic product’s preservative system can withstand microbial contamination over time. The test is meant to show what happens when people open a product over and over again, let it air out, and use it in dirty places.
PET, also known as challenge testing, is a key part of a cosmetic product’s microbiological safety assessment and is required for most cosmetic formulations.
The Role of PET in Cosmetic Safety
PET puts certain microorganisms into the product and keeps an eye on how well preservatives stop them from growing over time. It simulates real-life contamination situations to make sure your formula can be used over and over again without losing its microbiological integrity.
When Is PET Required?
When you need PET, it’s usually because:
- You’re making a new formula
- You’re changing or reformulating an old one
- The product has a lot of water in it
- It’s meant to be used over and over again (like creams, gels, and cleansers)
Every time a user dips into a jar or squeezes a tube—especially water-rich products—bacteria, mold, and yeast are introduced. PET ensures your preservative system is strong enough to prevent microbial growth over time.
Even “clean” or natural cosmetics must show that they are safe for microbes, especially if they don’t have many preservatives.
Why Cosmetic Products Need Effective Preservation
Preservatives protect your product from microbial contamination, which can compromise performance, consumer safety, and brand reputation.
Risk of Microbial Contamination in Cosmetics
Bacteria, mold, and yeast can get into a jar or tube every time a customer dips a finger in or squeezes the product out. Water-based products are especially vulnerable, so creams, shampoos, and lotions need to be preserved and PET used well.
Health Implications of Contaminated Products
Using cosmetics that are dirty can irritate your skin, give you an infection, or make you allergic. Even worse, they can cause your brand to lose customers or have to recall products. PET helps lower these risks by making sure that your preservation system is strong enough to keep the product safe for a long time.
Regulatory Requirements for PET
Cosmetic products sold in the EU must meet strict microbiological safety standards. PET is a key part of demonstrating compliance.
EU Regulation 1223/2009
To launch in the EU, cosmetic products must comply with Regulation (EC) No 1223/2009, which mandates microbiological safety documentation in the Cosmetic Product Safety Report (CPSR) (Annex I, Section 3). Challenge testing (PET) is commonly used to demonstrate preservative efficacy and regulatory compliance.
ISO 11930 Guidelines
ISO 11930 is the standard that everyone around the world uses for doing and understanding PET. It says what microorganisms should be tested, how often they should be tested, and what the results should look like (for example, log reductions in microbial counts).
Following ISO 11930 makes sure that your PET results are both scientifically sound and in line with the law.
How PET Is Performed: Step-by-Step
The procedure is complicated, but the goal is simple: show that your preservatives work when they are put to the test.
- Inoculation: The product is purposely infected with common test organisms.
- Sampling Intervals: Samples are taken every few days (for example, on days 7, 14, and 28).
- Analysis: We check the microbial counts to see if they have been lowered or gotten rid of completely.
Microorganisms Used in the Test
A common set of microbes used in PET is:
- Staphylococcus aureus
- Pseudomonas aeruginosa
- Escherichia coli
- Candida albicans
- Aspergillus brasiliensis
These organisms represent a broad spectrum of likely contaminants and are specified in ISO 11930
Interpretation of Results
If your product passes, it means it meets the ISO 11930 standards for microbial log reduction. If it doesn’t work, you may need to change the formula or use a stronger preservative system.
PET vs. Microbiological Testing: What’s the Difference?
It can be easy to mix up Preservative Efficacy Testing with regular microbiological testing, but they are not the same thing.
- Microbiological testing looks for microbial contamination that is already present in a batch of products.
- PET checks to see if the product’s preservative system can keep things from getting contaminated in the future.
Both are important, but only PET can tell you for sure that your preservative system is working long-term.
Which Products Require PET?
Preservative Efficacy Testing (PET), as outlined in Annex I, Section 3 of Regulation (EC) No 1223/2009, is a critical part of the microbiological safety evaluation required for all cosmetic products marketed in the European Union. While PET is generally mandatory, its necessity is determined based on the formulation’s susceptibility to microbial contamination and the conditions of use.
- Products that typically require PET include:
- Creams and lotions
- Shampoos and cleansers
- Facial masks
- Baby care products
Any product packaged in jars, tubs, or wide-mouth containers that are repeatedly exposed to air and skin contact. These products are especially at risk due to their water content, frequent handling, and high exposure to the environment.
Exceptions to PET (When May PET Be Omitted?)
Some cosmetic products may be exempt from PET if they present a very low risk of microbial contamination. According to ISO 11930:2019, PET may not be required for:
- Anhydrous formulations (e.g., oil-only balms or powders) that contain no water and therefore do not support microbial growth
- Single-use products that are immediately used after opening and are not reused
- Products manufactured, filled, and sealed in aseptic (sterile) conditions, provided they remain sterile throughout shelf life (aerosols)
- Products with a very high (>10) (bar soaps) or very low (<3) pH (exfoliators), depending on additional microbiological risk factors
However, these exemptions are not automatic. The decision must be justified within the Cosmetic Product Safety Report (CPSR) through a product-specific microbiological risk assessment. Factors considered include the formulation type, packaging, method of use, target population, and expected storage conditions.
For a more detailed breakdown of which products may qualify for exemption, see Certified Cosmetics Blog – Which Products Are Exempt from the Challenge Test?
Benefits of Conducting PET Early in Product Development
Not only is it smart to plan PET during early development, but it’s also cost-effective.
- Avoid expensive reformulations after the fact
- Cut down on regulatory delays
- Make the CPSR preparation go more smoothly
- Make safety and stability claims stronger for the product
Testing your preservative system early on can help you find problems before your product goes on sale.
Certified Cosmetics’ Approach to PET
At Certified Cosmetics, we use our deep scientific knowledge and regulatory expertise to do thorough testing of preservative effectiveness. Our team makes sure that your products are safe, stable, and ready for market, as well as compliant.
We help you with every step of compliance, from finding the right ingredients to getting CPSR support.
FAQs About Preservative Efficacy Testing
Q1. Do all cosmetics need PET?
Yes, unless the product is proven low-risk (e.g. anhydrous, single-use, or sterile) and supported by a valid microbiological risk assessment per ISO 11930.
Q2. Can natural cosmetics not have PET?
Even products that are “natural” or don’t have preservatives in them have to show that they are safe for bacteria. People still need PET a lot of the time.
Q3. How long does it take to get PET?
Usually 35-50 days, with a full test report with all the results.
Conclusion: A Crucial Step for Safer, Longer-Lasting Cosmetics
Preservative Efficacy Testing may take time, but it’s time well spent. It makes sure that your cosmetics are safe for people to use, protect them from harmful microbes, and are ready for sale, no matter where you sell them.
Check out our Preservative Efficacy Testing service or the Certified Cosmetics blog for more information on how to make products that are safe and legal.
