Two Types of Primary Carcinogens

A carcinogen is a substance or an exposure to a substance that can cause cancer in the body. Cancer occurs when cells mutate, meaning the DNA inside the cells is altered. When this happens, more mutated cells are produced when the original mutated cell multiplies. This is how tumors form. There are thousands of known, probable and possible carcinogens identified by science that fall into two main categories.

Naturally Occurring

• There are substances in nature that are known carcinogens. Examples include environmental radioation such as sunlight, which produces ultraviolet radiation that can cause skin cell mutations and/or skin cancer, and radon gas. Naturally occurring carcinogens can be found in many everyday items, including food. Many fruits and vegetables produce natural pesticides to ward off insects and fungi, and a great deal of those substances have been shown to be carcinogens. For example, mushrooms contain hydrazines and peanuts contain aflatoxin, both known, naturally occurring carcinogens.

Artificially Produced

• These are substances that are produced by man by mixing certain chemicals together, some of which are known carcinogens and some that may become carcinogenic when mixed with other chemicals. Common examples include cigarettes -- which contain 4,000 carcinogenic chemicals -- asbestos and radioactive compounds used to make chemotherapy treatments. Some chemicals even turn into carcinogens when they react with chemicals in our own bodies. Nitrites, which are preservative chemicals that are added to meats, become nitrosamines when they hit the digestive tract. Nitrosamines are a known carcinogenic substance. Man-made carcinogens can also find their way into our food and water supplies through pollution.

Known Carcinogens

• There are lists available from a variety of reputable sources of known, probable and possible human carcinogens. Different government, independent and/or international agencies also have different groups or scales they use to rank carcinogenic substances. The reason is that a substance may be carcinogenic, but substances have different levels of cancer-causing ability based on the intensity of its carcinogenic make-up, the level of exposure necessary to cause cancer, and other factors. Examples of organizations that have compiled comprehensive lists are the American Cancer Society, International Agency for Research on Cancer, National Toxicology Program and the Environmental Protection Agency.

Is It a Carcinogen?

• To determine if a substance is a carcinogen, scientists and researchers have to complete studies and tests that are not always easy or definitive, because they can't just expose humans to a suspected carcinogen and wait to see if it causes cancer. Scientists often use cell cultures or animals to test substances. They also look at the cell structures of substances and compare them to other known carcinogens to see if they are similar. Scientists will often compare the results of their lab studies and human studies that are usually conducted in people's natural environments before attempting to determine if a substance is a carcinogen.