The top failure causes are: preservative concentration too low, formula pH outside the effective range for the chosen preservative (many organics lose activity above pH 6.0), missing chelator such as EDTA, high free-water activity supporting microbial growth, and packaging or filling-line contamination. A cosmetic chemist with PET experience can audit your formula before submission. AJ Cosmo Labs connects you with those specialists through the iPhone app.
Read the full guide on Preservative efficacy testing →