The present paper reviews the carcinogenicity study of titanium dioxide（TiO2），widely used in the production of paints paper and plastics, as food additives and colorants, and increasingly, as nanpoparticles in pharmaceutical and cosmetics products, based on data published in openly available scientific literature. Increased incidence of tumors was reported in rats after exposure to respirable, fine or ultrafine TiO2 by inhalation or intratracheal instillation. No increased incidence of tumors was noted in mice or hamster after exposure to TiO2 by inhalation or intratracheal instillation, or in rats or mice given TiO2 by intraperitoneal or subcutaneous injection or by feeding. This review indicates that the incidence of tumors was increased in rats after inhalation or intratracheal instillation of TiO2 at levels associated with particle overload and persistent inflammation.
