Deborah Ippolito, age 15, of Columbia, Tenn.,for her question:
WHAT ARE CARCINOGENS?
Carcinogens are cancer causing agents. Most medical authorities agree that people develop cancer mainly through repeated or prolonged contact with one or more carcinogen.
Carcinogens attack normal cells and may eventually cause one of them to become cancerous. Scientists say that most cancers start this way—that is, with changes in a single cell. The changes are then passed on to all the cell’s descendants.
Some carcinogens are introduced into the body through the nose, mouth or some other opening. Others attack through a skin. Many cancers are probably caused by a combination of two or more agents rather than by a single one.
Laboratory tests and population studies indicate that two main groups of carcinogens can cause cancer in human beings: various chemicals and certain forms of radiation. Viruses make up a third group of suspected carcinogens.
Scientists have identified hundreds of chemicals that can cause cancer in animals. These chemicals are also a cancer hazard to human beings if they become widespread in the food supply, the general environment or the living or working environments of groups of people.
In most cases, a chemical carcinogen enters the food supply as a food additive or through use in agriculture. In discharging waste products, some factories release chemical carcinogens into the environment. Other chemical carcinogens may be found in the tars in tobacco smoke, certain industrial chemicals, certain natural food chemicals and certain chemicals in drugs.
Certain kinds of radiation produce cancer in people exposed to these radiations for long periods. Skin cancer, for example, can be caused by ultraviolet rays from the sun.
Also, experiments have shown that certain kinds of viruses cause cancer in animals. In samples of cancerous human tissues, scientists have found viruses similar to those that cause cancer in animals. But no evidence has yet been found that viruses can cause cancer in humans.
In the United States, cigarette smoking is responsible for nearly half the cancers associated with environmental agents. Cigarette smoking causes most cases of lung cancer and is associated with cancers of the esophagus, larynx, mouth, pancreas and urinary bladder.
Some industrial chemicals create a cancer hazard for people who work with them. Such chemicals include aniline dyes, arsenic, asbestos, chromium and iron compounds, lead, nickel, vinyl chloride and certain products of coal, lignite, oil shale and petroleum.
Unless industrial plants carefully control the use of escaping chemicals, excessive amounts may be released into the general environment. The chemicals may include carcinogens which can create hazards for people in surrounding areas.
Skin cancer occurs most often among sunbathers and people who work outdoors. Also, x rays are a cancer hazard if they are allowed to strike healthy tissue in large doses.
The usefulness of x rays in medical and dental diagnosis is believed to outweigh any hazards connected with their use. Also, careful exposure to the sun by sunbathers and outdoor workers should be problem free.