What is a carcinogen? Does a carcinogen always cause cancer? How worried do I have to be if I've been exposed to one?
The feeling that random contact with a normal, everyday substance might lead to cancer can be frightening. Yet, most people don't have a clear understanding of what it means, and whether or not they are going to get cancer.
I've had two recent questions about exposure to carcinogens. To address them we need to understand what we are talking about with carcinogens.
Nikhil Khanna posted this question: " Today we had some fried snacks which were wrapped in a newspaper... we noticed that the ink from the newspaper print was getting leached onto the snacks... I read on the Internet that newspaper print ink causes cancer and I got really worried... Will we get cancer because of this?"
A Facebook reader posted: "Today I bought around 7 strips of medicines (capsules and tablets) for my son that was packed in blister plastic packs and...they were exposed to the sunlight for around 2 hours. Should my son take those medicines, as I am scared of the blister plastic leaching harmful chemicals?"
First of all, a carcinogen does not cause cancer; cancer is caused by DNA mutations. It's a matter of random chance whether or not DNA damage occurs, and whether those mutations turn the cell into a cancer. A carcinogen can increase that chance of mutation and cancer initiation.
A person's risk of developing a cancer, then, depends on carcinogen, the type and amount of exposure, and their own genetic susceptibility (which you can't control).
There are only a few very strong carcinogens, and only a few exposures raise your cancer risk significantly. These include some chemicals and radioactive substances taken internally or breathed in, such as I131 exposure with nuclear fallout or nuclear testing. Even then, most people exposed do not get cancer. For example, it was estimated people exposed to the Chernobyl nuclear plant disaster had an estimated 3 to 4% above normal cancer levels. Other carcinogens are very strong -- such as the tars in cigarette smoke -- whereas other are very weak. Ingesting some substances are more likely to make you sick from toxicity or poisoning than getting cancer from it (such as arsenic, a strong carcinogen). The type of carcinogen impacts on kind of cancer that is at risk. For example, I131 from Chernobyl causes thyroid cancer since it is concentrated in the thyroid, whereas the tars found in cigarettes cause lung cancer.
A chance encounter on the skin or a very tiny amount ingested by accident is not likely to cause much harm. What is important, though, is repeated exposure to the chemical, such as in the workplace or in daily life. There are workplace guidelines. National Institute for Occupational Safety, NIOSH, and the Food and Drug Administration (FDA) may comment on exposure to a substance can increase cancer, and limit exposure to acceptable levels.
If you know a substance increases cancer risk, then you will want to avoid excessive exposure, or at least weight your risks. Exposure does not guarantee you will get cancer--not every smoker gets lung cancer, but smokers are 23 times more likely to get cancer. The choice will be up to you.
That of course brings up the question of what is a carcinogen, and how strong is it. Just because a compound is a "chemical" does not mean it is a carcinogen--even safe, natural substances such as vitamins have chemical structure that look like they should be unsafe--such as Vitamin B12--but in fact they are necessary for life! The IARC -- International Agency for Research on Cancer, a part of the World Health Organization--keeps details lists of carcinogenic compounds, classifying them from "known" to "possibly" to "probably not." For many substances there is no hard data, and you can't really know--you can't test it on people, and testing on animals does not always give the same results. So a lot of things are classified as probably possibly unknown.
We are continuously exposed to things that can slightly increase our risk of cancer, and it is impossible to avoid them all or we wouldn't be able to eat or breathe. All in all, most cancers arise from random mutational events, not from carcinogens. There are many other things to be more worried about than getting cancer from your surroundings.
To answer Nikhil Khan, most newspaper inks are now soy based and non-toxic. In they past, newspaper inks contained heavy metals, which are both toxic and mildly carcinogenic; some glossy magazines still require these inks. Even if these were toxic inks, the level of exposure you might have had is so minimal I would not worry about it. I would, however, ask the food vendor to use plain paper because the ink on food is unsightly and spoils your appetite.
To the Facebook reader, I wrote that I would be more concerned that the medicine itself was deteriorating due to the exposure, and it might not maintain its potency. But still 2 hourse is hardly enough time for any significant breakdown to occur, and it takes a lot of PVC to even slight increase the risk of cancer (most pill blister packs are made of PVC).