Adequacy of cosmetic preservation: chemical analysis, microbial challenge and in-use testing

Synopsis The adequacy of preservation of seven previously unopened commercial cosmetic products was tested by individual challenges with Aspergillus niger ATCC 9642, Candida albicans ATCC 10231, Escherichia coli ATCC 8739, Pseudomonas aeruginosa ATCC 15422, and Staphylococcus aureus ATCC 6538, using the Cosmetic, Toiletry, and Fragrance Association (CTFA) method. Each product was consecutively challenged three times, 28 days apart. Inoculated composite products were counted by conventional techniques at eight prefixed intervals. Six of seven cosmetics passed the CTFA acceptance criteria. On the basis of viable counts seven days after inoculation (CTFA criteria), the products were classified as follows: five products were well preserved, one was marginally preserved, and one was poorly preserved. The poorly preserved product failed the CTFA criteria for all three bacteria tested. Concentrations of preservative ingredients in uninoculated composites were determined by high performance liquid chromatography. All preservatives listed on the labels of the seven cosmetic products were identified by chemical analysis. Tentative in-use validation of the CTFA criteria was performed for three of the seven cosmetic formulations. The results suggested that some cosmetic products may be underpreserved.