Live in a smoggy city — or just visited one for a few days? A new study suggests that polluted air can change our DNA in just three days, increasing your chance of getting cancer and other diseases.

The downer news comes from a study that looked at the DNA of steel-foundry workers in Brescia, Italy, who were exposed to particulate matter — teensy pieces of soot, dust and metal in the air — similar to those found in “normal air” in cities.

How does this DNA change occur? The process is complicated. National Geographic describes it thusly:

Exposed workers’ DNA was damaged by a slowed rate of “methylation,” a biological process in which genes are organized into different chemical groups.

Fewer groups means that fewer genes are expressed — or made into proteins — a crucial process in the body’s regular maintenance.

The researchers behind the study say that more study is still needed — but we don’t need to wait for confirmation to start cleaning up our air. The American Lung Association’s recommended steps to clean up the air in your neighborhood are: “drive less; don’t burn wood or trash; use less electricity; and make sure local school systems require clean school buses."