ISO 21149:2017

Overview

ISO 21149:2017 - "Cosmetics - Microbiology - Enumeration and detection of aerobic mesophilic bacteria" provides general guidelines for detecting and counting aerobic mesophilic bacteria in cosmetic products. The standard covers two main approaches: quantitative colony counts on agar (plate count) and presence/absence detection after enrichment. It also requires demonstration of the neutralization of any antimicrobial properties of the product so viable organisms can be recovered.

Key topics and technical requirements

• Scope and applicability
  • Applies to a wide range of cosmetic products but may be unsuitable for some formulations (e.g., certain water‑immiscible products). Alternative or automated methods may be used if their equivalence is demonstrated.
• Sampling and samples
  • Defines sample and initial suspension (minimum sample portion: at least 1 g or 1 ml) for preparing dilutions.
• Principal methods
  • Plate count (pour or spread plates) using a non‑selective agar, followed by aerobic incubation at 32.5 °C ± 2.5 °C for 72 h ± 6 h, then enumeration of CFU.
  • Membrane filtration for suitable samples, with transfer of membranes to agar for incubation and counting.
  • Enrichment-based detection for absence/presence testing when low counts are expected.
• Neutralization and suitability testing
  • The standard requires neutralizers/diluents and suitability tests (Clause 13) to confirm neutralization of preservatives or antimicrobial activity and validate counting/detection methods for the specific product.
• Procedure and reporting
  • Detailed procedural elements (preparation of suspensions, dilutions, incubation, colony counting, expression of results and interpretation) are specified. Results may require further identification of isolates using referenced identification standards.
• Risk-based applicability
  • Advises performing a microbiological risk analysis to determine which products require testing. Products with low microbiological risk (see ISO 29621) may be treated differently.

Practical applications and users

• Who uses ISO 21149:2017
  • Cosmetic manufacturers, quality control laboratories, contract testing labs, regulatory authorities and safety assessors.
• Why it matters
  • Ensures consistent, reproducible methods for assessing microbial quality and consumer safety, supporting release testing, stability studies, contamination investigations and supplier qualification.
• When to apply
  • Routine QC testing, batch release, validation of preservative efficacy and when troubleshooting contamination or validating alternative microbiological methods.

Related standards

• ISO 29621 - Guidance on low microbiological risk cosmetic products
• ISO 21148:2017 - General instructions for microbiological examination of cosmetics
• EN 12353 - Preservation of test organisms for antimicrobial activity testing

Keywords: ISO 21149:2017, cosmetics microbiology, enumeration aerobic mesophilic bacteria, plate count, membrane filtration, enrichment, neutralization, CFU, microbiological risk analysis.