If you live in the city, you likely exist in a cloud of smog — or at least inhale some level of air pollution on a daily basis. Perhaps you’ve gotten so used to it that the wheezing feeling in your chest or the street dust in your eye feels like second nature.

New research, however, aims to investigate what actually happens in your lungs on a molecular level when you breathe in smog. The study, completed by researchers at the University of Melbourne, examined how ozone impacts the lungs through models of lung proteins in the lab.

Using a mass spectrometer, the researchers took the amino acid cysteine (which makes up lung proteins) and mixed it with ozone molecules in a controlled environment. They found that the cysteine was “radicalized” in the presence of ozone, producing an instantaneous effect — and unleashing free radicals, atoms or molecules that contain an unpaired electron and are highly reactive. Free radicals are associated with oxidative damage and aging, and are typically bad for your health. In short, the ozone or smog interacted with the lung proteins negatively, creating free radicals that are known to be damaging to human health.

“No one had really noticed that you can form free radicals in the reaction of proteins with ozone, and since these are highly reactive species, you don’t want them around,” Professor Richard O’Hair, an author of the study, said in the press release. “Free radicals can unleash fury and cause many chemical transformations. If they get out of control, they can just chew through a system and destroy it.”

Past research has found a link between an accumulation of free radicals and an increased risk of heart disease and some cancers. “So when free radicals are formed in the body, such as the lining of the lung, damage occurs, that may ultimately result in inflammation and breathing difficulties,” O’Hair said in the press release.

For the most part, scientists already know that air pollution is harmful to health — one recent study found that air pollution contributed to a person’s risk of heart disease and early death. Air pollution has also been linked to cancer, respiratory disease for nonsmokers, and “silent stroke.” But it’s not until now that scientists have delved into understanding the impact of ozone on lungs on a molecular level. Of course, the study was completed in the lab — the researchers will need more information on how the same chemical transformations occur in the human body.

In the meantime, the researchers argue that we should do all we can to reduce air pollution — or at least avoid it. “If there is free radical damage to lung proteins, it’s unlikely to be reversible, so you won’t be able to design a magic-bullet drug to undo the damage,” O’Hair said in the press release. “Ozone is the result of pollution. So the message has to go out that we need to be proactive on reducing smog levels and pollution.”

Source: Khairallah G, Maccarone A, Pham H, Benton T, Ly T, Silva G. Radical Formation in the Gas-Phase Ozonolysis of Deprotonated Cysteine. Angewandte Chemie International Edition, 2015.