The detection of germs in a cosmetic product always requires special attention. Contaminated raw materials, deficiencies in manufacturing, or even contamination of packaging materials can be causes.

Regardless of the detected quantity, identification should always be carried out. Only in this way can a risk assessment be conducted based on the number of microorganisms combined with the type of germ (risk group, hazard potential). This allows the question of the product's marketability to be answered.

Additionally, within the framework of a microbiological risk management system, one obtains information about possible sources of entry with the aim of avoiding similar contaminations in the future.

The requirements for microbially low-risk products are described in the standard ISO 29621 "Guidelines for the risk assessment and identification of microbiologically low-risk products". 

These are products that, due to their physicochemical properties, inhibit the growth of microorganisms or kill them.
These are products that meet one or more of the following requirements.

• pH-value: <3
• pH-value: >10
• anhydrous products
• alcohol content: >20%
• filling temperature: >65°C
• water activity: <0.75
• solvent-based products
• oxidizing products
• aluminum chlorohydrate content: >25%

Other low-risk products can be identified as part of an individual risk assessment.
For microbiologically low-risk products, a preservative efficacy test is not necessary as part of the safety assessment.

For the microbiological examination of cosmetic products, there are several ISO standards that describe the corresponding methods. 

• ISO 21149 Counting of aerobic mesophilic bacteria
• ISO 16212 Counting of yeasts and molds
• ISO 18415 Detection of specified and non-specified microorganisms
• ISO 18416 Detection of Candida albicans
• ISO 21150 Detection of Escherichia coli
• ISO 22717 Detection of Pseudomonas aeruginosa
• ISO 22718 Detection of Staphylococcus aureus
  
  Further standards that include the microbiology of cosmetic products are 
• ISO 11930 Evaluation of antimicrobial protection
• ISO 19838 Guidance on the application of ISO standards in the field of microbiology
• ISO 17516 Microbiological limits

The two variants of the preservative efficacy test differ in some aspects of the methods and assessment criteria. For implementation according to ISO 11930, the following applies:

• the microbial status of the product must be checked before implementation
• Escherichia coli is required as an additional test organism
• a different nutrient medium (Potato Dextrose Agar) is prescribed for Aspergillus brasiliensis
• the procedures for preparing the microorganism cultures are newly regulated
• there are no requirements for microbial reduction after 2 days
• there are different requirements for the yeast Candida albicans and the mold Aspergillus brasiliensis
• a margin of 0.5 log levels is permissible to account for measurement uncertainty
• Criterion A and B no longer have the same significance

Further information on the two types of challenge tests can be found in the BAV Newsletter Cosmetics Part 3 (available at https://www.bav-institut.de/files/newsletters/Sondernewsletter-Kosmetik-Teil-3-in-2013.pdf ).

The purpose of the preservation challenge test is to confirm that the cosmetic product, when used as intended, prevents microbial growth and is thus microbiologically stable. However, it should be noted that preservation challenge tests are merely models and do not guarantee 100% safety.
The execution of a preservation challenge test is required by the EU Cosmetics Regulation as part of the safety assessment (see Annex I, Point 3 of the Regulation).
Exempt from the requirement to conduct a preservation challenge test are products that meet one or more of the following conditions.

• pH value: <3
• pH value: >10
• water-free products
• alcohol content: >20%
• filling temperature: >65°C
• water activity: <0.75
• solvent-based products
• oxidizing products
• aluminum chlorohydrate content: >25%

Other low-risk products may be identified as part of an individual risk assessment.

The specified microorganisms are described in the ISO 17516 standard. These microorganisms must not be detectable in cosmetic products. They include the three bacteria Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, as well as the yeast Candida albicans.