How do carcinogens cause cancer?

News articles over the past few years have implicated everything from sunlight’s ultraviolet radiation to burnt toast as potential carcinogens, or cancer-causing substances. So, should you be rushing to cut these everyday exposures out of your life? Well, it depends on the material you are talking about, and how much and how often you are in contact with it.

The first steps in the transformation of a normal cell into a cancerous cell happen at the level of the DNA, a remarkably complex foundation for our normal functions; in three billion individual nucleotides (the alphabet of DNA’s code), it encodes all the instructions required for any cell to survive.

But as cells divide and pass down their DNA, these instructions have to be re-copied each time. It’s pretty hard to make perfect copies each time (just try typing out War and Peace without making any typos.) With billions of new cells produced in an individual each day, there are a lot of opportunities for error. And when those mistakes happen in the parts of the genome that code instructions for processes like cell replication, you can end up with a cell that grows abnormally quickly.

However, when it comes down to it, many carcinogens do pose a real risk. Take smoking, for example. The most important thing you can do to decrease your risk of cancer is to quit smoking, says Susan Gapstur, vice president of the Epidemiology Research Program at the American Cancer Society. That advice is based on years of correlational studies that found increased rates of lung cancer in people who also smoked cigarettes as well as studies looking at the effects that the chemicals in cigarettes can have on cells’ DNA.

This disparity is a root cause of much of the confusion around carcinogens, some experts say. Despite what it might seem like, not everything causes cancer, says Jakob Jensen, associate dean and professor of communications at the University of Utah. From his work in cancer communications, Jensen has found that the widespread conception that carcinogens are everywhere makes people feel like it’s out of their control and that there’s nothing they can do to decrease their risk of developing cancer. But that’s not true.

Exposures to these “agents of evil” can cause some wacky changes to our cells that lead to cancer. For example, some carcinogens can directly cause genetic mutations that foster abnormal cell growth and tumors. Others don’t attack our genes directly, but trick our cells into cell division overdrive. That excess division then leads to potential genetic mutations down the road.

Does this mean that any exposure to a known carcinogen will cause you to develop cancer? The candid answer is, “It depends.” For one, our genes are under continual attack by genetic mutations, but our DNA usually does a stellar job of repairing itself. That said, though, that “repairman” skill isn’t equal among all of us. Some of us do a better job of repairing our genes than others, which means that some people are more naturally susceptible to the negative effects of a carcinogen. Furthermore, a carcinogen’s link to cancer can depend on:

  • Age and gender
  • Potency: Some carcinogens require pretty heavy exposure to be dangerous, while others are linked to cancer with just a brief exposure.
  • Exposure type: For example, were you exposed to a carcinogen one time or continually over a period of years?

A glance at the list of carcinogens might initially overwhelm you and as just one individual, you will never need to worry about all of them. Ever heard of 1,2-Dichloropropane? It’s a byproduct of making dry cleaning chemicals, so unless you work in the chemical manufacturing industry, you probably don’t have to worry about it. Many of the items listed are used in manufacturing, and some are more dangerous than the items they turn into (for example, vinyl chloride can cause liver cancer, but is safe once it is turned into solid PVC pipes, found in many homes). A number of them are actually drugs, some of which actually treat cancer itself.