Zinc oxide nanoparticle

The exact physical and chemical properties of zinc oxide nanoparticles depend on the different ways they are synthesized.

Because they are very tiny, nanoparticles generally can travel throughout the body, and have been shown in animal studies to penetrate the placenta, blood–brain barrier, individual cells, and their nuclei.

However, human skin is an effective barrier to ZnO nanoparticles, for example, when used as a sunscreen, unless abrasions occur.

ZnO nanoparticles may enter the system from accidental ingestion of small quantities when putting on sunscreen.

When sunscreen is washed off, the ZnO nanoparticles can leach into runoff water and travel up the food chain.