Zinc oxide (ZnO) appears as a promising preservative for pharmaceutical or cosmetic formulations. The
other ingredients of the formulations may have specific interactions with ZnO that alter its antimicrobial
properties. The influence of common formulation excipients on the antimicrobial efficacy of ZnO has
been investigated in simple model systems and in typical topical products containing a complex
formulation. A wide variety of formulation excipients have been investigated for their interactions with
ZnO: antioxidants, chelating agents, electrolytes, titanium dioxide pigment. The antimicrobial activity of
ZnO against Escherichia coli was partially inhibited by NaCl and MgSO4 salts. A synergistic influence of
uncoated titanium dioxide has been observed.