These mutations are either inherited or acquired. There is usually a latency period of years or decades between exposure to a carcinogen and the appearance of cancer. This, combined with the individual nature of susceptibility to cancer, makes it very difficult to establish a cause for many cancers. Dietary components, like excessive consumption of alcohol or of foods high in fat and low in fiber rather than fruits and vegetables that contain antioxidants and necessary micronutrients, have also been linked with various cancers. Some cancers may be triggered by hormone imbalances.
Aflatoxins are natural mold byproducts that can cause cancer of the liver.
Certain carcinogens present occupational hazards. Benzene and vinyl chloride are other known industrial carcinogens. Exposure to the ultraviolet radiation of sunlight is the leading cause of skin cancer . Many other substances have been identified as carcinogenic to a greater or lesser extent, including chemicals in pesticides that leave residues on foods. In the early 20th cent., the American virologist Peyton Rous showed that certain sarcomas affecting fowl could be transmitted by injection of an agent invisible under the microscope and later indentified as an RNA-containing virus.