Objective To evaluate the inhibitory effect of online-sold “preservative-free” cosmetics against contaminated microorganisms during storage and use, to establish a method for assessing the preservative efficacy of such cosmetics, and to provide data support for the formulation of relevant standards.

Methods A total of 16 batches of cosmetics claiming preservative free were collected to determine their pH value, water activity, total aerobic microbial count (TAMC) and total molds and yeasts count (TYMC). Meanwhile, preservatives not listed in theSafety and Technical Standards for Cosmetics (2015 edition) (referred to as “unlisted preservatives”) were screened. In addition, a preservative challenge test was conducted on these cosmetics.

Results All the 16 batches of samples were generally weakly acidic, and with a water activity ≥0.6, which were suitable for microbial growth. Unlisted preservative not labeled on the package was detected in one batch of cosmetic. The results of neutralizer verification showed that three batches required further dilution to eliminate the antimicrobial interference. After inoculation with challenge microorganisms and cultivation for 7 days, two batches of cosmetics did not achieve a bacterial reduction rate of 99.90%, and the fungal reduction rate did not reach 90.00% either. While another two batches of cosmetics experienced microbial growth during testing, indicating a failure of the preservative challenge test. The overall pass rate was 75.00%.

Conclusion Some online-sold preservative free cosmetics have insufficient preservation efficacy and pose a certain risk of microbial contamination.