Yesterday, the International Agency for Research on Cancer (IARC), an expert organization of the World Health Organization, announced their determination that air pollution is a known cause of cancer. Traditionally, cancer-causing agents, or carcinogens, are substances, like lead, or come from single sources, like cigarette smoke. Exposure to carcinogens is often avoidable, or controllable – which is why smoking is no longer allowed in restaurants, on airplanes, and in workplaces, in some parts of the world. It is also why lead is no longer allowed in gasoline or paint.

What is complicated about this story is that air pollution is made up of a mixture of substances, and comes from a mixture of sources, making it challenging to control, and, nearly impossible to avoid. Air pollution has many sources, including transportation, electricity generation, and other types of energy use, such as cooking, or manufacturing, that involve combustion, burning and release of gases and particles. Some of us are sensitive to air pollution, either in the form of allergy, asthma, cardiac effects or irritation. While the announcement of a link to cancer is significant, it’s not entirely unexpected.

The U.S. Environmental Protection Agency (EPA) has for years assessed the health risks from air pollutants, including some 80 substances considered to be cancer-causing. Their most recent assessment estimates that most Americans (285 million people) have an increased lifetime chance of one in one million of getting cancer from air pollution. This is similar to the odds of getting struck by lightning, or winning the lottery. About 14 million people in the U.S. are predicted to be at higher risk, in the range of 1 in ten thousand (a 0.01 % chance) risk of getting cancer from a lifetime of exposure to air pollution. Considering the overall odds of getting cancer in one’s lifetime are more than in in 3 (33%), this additional risk is pretty low – instead of 33% it is 33.01% for people in more polluted areas, and 33.0001% for the rest of us.

In the U.S., a lot has been done to reduce sources of air pollution, and the risks are low. But they are not zero. We can’t reduce the risk from air pollution to zero. It is just not possible to simply avoid air pollution. We are all exposed to it, at some level. No matter how careful we are, we can never get to zero. Every time we get in a car, climb a flight of stairs, eat in a restaurant, ride a bike or cross the street, we are assuming some risk to our health and to our safety. Life is full of risks, and we can never live without risk. Some risks we choose, like risking illness from eating raw oysters, and some risks we don’t, like air pollution.

My dear friend Ellen was just treated for throat cancer, and told me she is now intolerant of cigarette smoke. As a non-smoker, who does not live with a smoker, she is not exposed to much smoke to begin with. Avoidance is easy enough – cross the street, avoid places where smokers gather. But now, I expect she is also going to be concerned about her exposure to air pollution. There are some choices we can make individually, like to live in a place with lower pollution levels, avoid spending lots of time in traffic, ensure not living or working downwind of major pollution sources like power plants. She may not want to burn a lot of wood in her fireplace, or be exposed to other types of open burning (leaves, trash).

Each of us contributes to air pollution –when we cut the grass, or drive cars and trucks, use dirty heating and cooking sources (wood burning, coal, oil) or even when we use electricity (unless we are 100% reliant on wind or solar power). Even those of us off-the-grid, who use wood burning stoves or kerosene heaters, are emitting particles into the air that are now agents associated with cancer.

Beyond that, air pollution does not have individual boundaries. The real significance of the IARC designation is in the implications globally. Individuals can’t fully mitigate exposure to air pollution, it requires collective action. We need international cooperation and regional solutions – for example drastically reducing the use of fossil fuels for electricity. upgrading diesel generators to cleaner equipment  - that extend beyond geographic boundaries.   While we can individually control how much pollution we each generate, this only solves part of the problem. Hopefully, the IARC designation will motivate international action to address those truly at risk, and lower our risks in the process.