UnitedStates Pharmacopeia (USP) Challenge Test

USP 51 - Antimicrobial Effectiveness Test

This Preservative Efficacy Test (PET) or Cosmetic challenge test, is essential for assessing the safety of water-based cosmetic products. It is most commonly used for products sold in the United States but is recognised worldwide.

UnitedStates Pharmacopeia (USP)

'USP 51 - Antimicrobial Effectiveness Test'

Sometimes referred to as USP 51 or 'USP Challenge test'

It is a Preservative Efficacy Test (PET) that is adapted to cosmetic products to ensure they are safe for consumers in the United States.

USP Cosmetic Challenge Testing

  • Which USP Test?

    Topical: These are cosmetics and personal care products such as creams, lotions, shampoos and skin cleansing products.

    Oral: Products that are intended to be used for oral care that make contact with teeth or the inside of the mouth, such as toothpaste and mouthwash.

    Wet Wipe: Products such as facial cleansing wipes, sheet masks and wet wipes. The price differs due to the additional processing steps, which add complexity to the procedure.

  • How Long?

    We estimate:

    USP test approximately 5-6 weeks.

    Double USP approximately 7-8 weeks.

    The time frame is from when we receive the sample and testing has been initiated to when we issue the final report with any relevant documentation to be included.

  • Test Procedure

    We require a minimum sample size of 250 g to conduct a full challenge test.

    Cosmetic samples will be inoculated with the various test microorganisms and microbial counts are taken at set intervals of 14, and 28 days. To ensure that the samples comply with the criteria for the United States Pharmacopeia (USP) we use the 'plate count method' to determine the number of colony-forming units (CFU) which indicates the remaining viable cells within the product. If the product is effectively preserved, microbial growth will be constrained.

EP, USP or ISO 11930?

  • EP USP ISO
    UK ● ○
    EU ● ○
    USA ●
    World ● ○ ○

    ● Recommended
    ○ Acceptable (customer dependant)

    EP - European Pharmacopoeia - 5.1.3 “Efficacy of Antimicrobial Preservation"
    USP - United States Pharmacopeia - Chapter 51 “Antimicrobial Effectiveness Testing”
    ISO - ISO 11930 - “Evaluation of the antimicrobial protection of a cosmetic product”

  • When selling cosmetic products, it is crucial to comply with the regulatory requirements of the country in which the product is being sold. For cosmetics, the quality and safety standards are typically determined by one of three major standards: the European Pharmacopoeia (EP), the International Organization for Standardization (ISO), or the United States Pharmacopeia (USP).

    Each of these organisations sets different standards for product testing and quality control, so it is important to choose the appropriate standard for the country in which you are selling your product. For example, if you are selling your product in Europe, you may need to comply with EP standards, while products sold in the US may need to meet USP standards.

    Choosing the right test and certification standard can help ensure that your product is safe and effective, and that it complies with local regulations and standards.

PET Test Details

  • EP USP ISO
    Incubation (days) 28 28 28
    Sample required (g) 250 250 250
    Total Species 4/5 5 5
    Staphylococcus aureus ● ● ●
    Pseudomonas aeruginosa ● ● ●
    Candida albicans ● ● ●
    Aspergillus brasiliensis ● ● ●
    Escherichia coli ○ ● ●

    ● Required
    ○ Optional (Oral products)

    EP - European Pharmacopoeia - 5.1.3 “Efficacy of Antimicrobial Preservation"
    USP - United States Pharmacopeia - Chapter 51 “Antimicrobial Effectiveness Testing”
    ISO - ISO 11930 - “Evaluation of the antimicrobial protection of a cosmetic product”

  • The major differences between the methods are noted in the table opposite.

    The European Pharmacopoeia (EP) is the most stringent test method among all our test method options. This traditional test method is recognised across the glove universally and is always the safest option if in doubt.

    For oral care products, testing against Escherichia coli is an additional requirement of the EP method.

    The ISO 11930:2019 method uses less stringent pass criteria compared to the other pharmacopoeia methods.

    The cost of a cosmetic challenge test varies by the type of test chosen as well as the addition of any other microorganism cultures.

    We also offer the option to conduct a ‘double’ United States Pharmacopoeia where the samples are inoculated again with the required microorganisms after 14 days to ensure that the formulation is able to withstand even tougher microbial conditions.