CTFA M-4 Method Summary

Preservative challenge testing for eye area cosmetics is extremely important to ensure the safety of your consumers. The eyes are a common area for infection by microorganisms such as Pseudomonas species that can be found in cosmetics that are not properly preserved. CTFA M-4 is a guideline for preservative challenge testing of eye area cosmetics.

A summary of the CTFA M-4 method is described below:

  • The product is separated out into 5 containers, each being challenged with one of the 5 method-specified microorganisms (S. aureus, E. coli, P. aeruginosa, C. albicans, and A. brasiliensis) at fairly high concentrations.
  • The initial concentration of each microorganism is determined by standard dilution and plating techniques.
  • A separate aliquot of the product is diluted along with a control substance, to be used in the neutralization and recovery validation to verify that the methods and media used are sufficient to recover the microoganisms.
  • The product is held at room temperature for a period of no less than 28 days.
  • The product is evaluated at specific intervals within the 28 day period. Sampling is recommended immediately after inoculation and at least 2 of the following days: 2, 7, 14, 21, and 28 days.
  • Test sample colonies are counted at each specified interval to determine the amount of microorganisms remaining.
  • The log reduction of each microorganism at each interval is reported.
  • OPTIONAL: The product is separated into fewer containers and mixed culture inoculations are used.
  • OPTIONAL: The product is re-inoculated with even more microorganisms and allowed a longer incubation period (specified by study sponsor). Sampling occurs weekly for up to 3 weeks following reinoculation.
  • For eye area cosmetics that are not water-miscible, such as pressed powders,emulsions, etc., see our CTFA M-6 summary page for atypical cosmetics.


1. Cosmetic, Toiletry, and Fragrance Association 2007. “CTFA Microbiology Guidelines”

For more information regarding CTFA M-4 testing or to set up a test just contact the lab or request a price quote.