An over-the-counter medicated foot powder contains camphor, eucalyptus oil, lemonoil, and zinc oxide. Only one of the ingredients is antimicrobial. Which one? How does it act against fungi?

The zinc oxide is the antimicrobial in the foot powder. The zinc interacts with sulfur atoms in proteins, denaturing the proteins and destroying their function.

Zinc oxide is the antimicrobial in the medicated foot powder.

Explanation:

Zinc oxide (ZnO) is used to treat several skin conditions such as acne, dermatitis, eczema, etc because it has antibacterial and antifungal properties. This property of the ZnO depends on its size i.e., the smaller the size of ZnO, the stronger antimicrobial activity it has. So, the ZnO nanoparticles are more efficient.

The zinc oxide interacts with the sulfur atoms in microbial proteins and denatures them and destroys their function. This action completely inhibits microbial growth. The treatment with zinc oxide causes the reduced production of conidia in fungi, damages their hyphae and inhibits their ability to produce mycotoxins.

The compounds containing zinc such as ZnSO4, Zn(ClO4)2, etc also have antifungal and antimycotoxin properties that can cause changes in the fungi cell structure. Also, the free radicals formed on the surface of the ZnO nanoparticles can cause damage to the lipids in the bacterial cell membranes that can lead to the leakage and breakdown of the bacterial cell membranes.