ISO 11930:2019 is the current international standard and is required for EU market entry. The older CTFA D5-81 protocol (also called USP 51) is still accepted by many US retailers. Both expose your formula to specific bacterial and fungal strains over 28 days and measure colony-forming unit reduction. A cosmetic chemist specializing in natural systems will recommend the right protocol based on your target markets and retail channel requirements.
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