Pollution can change your DNA in three days.

From National Geographic:

Breathing in polluted air may wreak havoc on our DNA, reprogramming genes in as few as three days and causing increased rates of cancer and other diseases.

So says a new study that tracked DNA damage in 63 steel-foundry workers in Brescia, Italy, who, under their normal factory conditions, were exposed to particulate matter.

The same damage may occur in city dwellers exposed to normal air, the researchers say.

Particulate matter includes suspended, tiny bits of dust, metal, or soot in the air, which can lodge deep in the lungs. Exposure to the substance has been linked to respiratory diseases, lung cancer, and heart problems.

Scientists know little about how inhaling particulate matter can cause health problems, according to lead study author Andrea Baccarelli of the University of Milan.

But they did find that exposed workers' DNA was damaged by a slowed rate of "methylation," a biological process in which genes are organized into different chemical groups.