Abstract
Natural and synthetic fibrous materials are widely used in construction, industrial applications, and biomedical devices, as well as in consumer products. Fibrous materials are chemically and structurally diverse; however, for regulatory purposes, fibers are defined on the basis of their size and shape. Widely varied natural and synthetic fibers are currently in commercial use or under development, suggesting the need to understand the potential for adverse health effects if respirable fibers were released during production or application. In contrast to asbestos or synthetic vitreous fibers, other types of fibers have not been systematically assessed for carcinogenicity using lifetime rodent inhalation assays because these tests are technically demanding, expensive, and require large numbers of animals.