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Carcinogenicity is a term applied to anything that has a demonstrated tendency to cause cancer, particularly in humans. A carcinogen is something that has the property of carcinogenicity. Carcinogens exist in several different forms. Some are substances such as those found in cigarettes and grilled or barbecued meats while others exist in the forms of radiation, such as that emitted from atoms with unstable nuclei. Carcinogens cause cancer, which is often deadly, by causing uncontrolled cellular growth and division that leads to the formation of deadly tumors that can spread throughout the body.
There are many different substances, natural and artificial, that have carcinogenic properties. Various naturally occurring fungi, bacteria, and viruses, for instance, are able to cause cancer and are thus said to have carcinogenicity. Many different sources of carcinogenicity are either man-made or related to the human use of natural substances. Smoking cigarettes, for instances, exposes one's body to many different cancer-causing agents. Different food preparation methods, such as grilling, frying, and barbecuing, also can induce carcinogenicity in some foods.
Some studies have shown that human habits and behaviors can have an inherent level of carcinogenicity. Staying awake through the night, for instance, affects the chemical balance in the human body in a way that may lead to or promote cancer. Such behaviors or habits that promote cancer usually fall into the category of "circadian disruption," meaning that they are behaviors that disrupt the normal, healthy cycle of sleep and wakefulness that people are supposed to go through on a daily basis.
The degree to which something is regarded to be carcinogenic, or the "level of carcinogenicity," is measured based on a variety of different systems. Some systems have very few classifications and are based only on whether or not a substance can cause cancer. Others have more classifications, such as whether the substance is known to induce cancer in animals and whether it is possible to make a judgment about its cancer-inducing potential at all. It should be noted that "carcinogenicity" is generally used to refer to whether or not something can cause cancer and is not usually used to compare the cancer-causing potential of different substances.
Many carcinogens damage an animal's DNA, thereby causing the uncontrolled cell growth that leads to cancer. Some substances, while not able to cause cancer themselves, can promote the growth of cancerous tumors and are still sometimes classified as carcinogens. Such substances are often hormones or other substances that can promote cellular growth.
@robbie21 - I don't really know they define a carcinogen. I'm guessing that it involves a combination of laboratory testing and real-world observation, when possible. It must be a matter of opinion as well as fact, because there seems to be disagreement. Have you ever seen those labels that say something like, "This product contains ___, a substance known to the state of California to cause cancer." Apparently, California knows things the federal government doesn't!
The short answer is that you can't protect yourself from the next big "oops." There are sensible things we can all do, like eating less packaged, processed food. (Many cans, for instance, are lined with BPA, which is not a carcinogen but is an endocrine disruptor.) I use vinegar and water instead of harsh cleaners.
And then--stop thinking about it. Just stop, or you'll make yourself crazy!
How do scientists really know what is carcinogenic and what isn't? I guess some things are fairly obvious; sun exposure can lead to skin cancer, exposure to cigarettes can lead to lung cancer, etc. But obviously, not everything that causes cancer in lab animals will cause cancer in people and vice versa.
So what about all those thousands of chemicals that are around us all the time? People used to think asbestos was safe! How can we protect ourselves from the next big "oops"?
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