Zinc is a nutrient with essential roles in tissue proliferation, differentiation, growth, functional maturation and systems of repair following injury. As a component of at least 300 essential enzymes and metalloproteins, the influence of zinc deficiency through dietary or hereditary causes (including acrodermatitis enteropathica) has been widely researched. Zinc oxide is a cause of mild oxygen stress through release of reactive oxygen radicals, but metallic zinc and soluble zinc compounds have shown negligible mutagenicity and clastogenicity in cell cultures or bacterial tests. Available evidence is insufficient to label zinc as a cause of human cancer following dietary overload, dermal exposure or chronic inhalation of metallic zinc dusts, zinc oxide or nanocrystalline particles in industry. Inhalation of zinc dusts is a cause of zinc fume fever and respiratory distress. The human prostate is a highly zinc-dependent organ but no evidence is seen to show that excessive zinc ingestion is a cause of prostatic carcinoma. Studies in chicken, rats, mice and hamsters have shown that intra-testicular injection of zinc chloride or sulfate induces a low incidence of testicular teratoma and embryonal carcinoma, but these are conditional upon the period of testicular maturation and hormonal status. Lifetime studies in rats receiving high dietary zinc have not shown significantly significant increases in tumour incidence, although a marginal increase in hepatoma may be a motive for further research.