People and animals have to inhale oxygen to live. About 18 percent of the air we breathe is O₂—two oxygen atoms that live happily together.

Ozone—O₃—has an extra oxygen atom, and the three of them don't live together very peacefully. They like to yank electrons out of other chemical compounds, including some that make up your lung cells.

These compounds are left damaged—just like you would be if somebody yanked off your arm. So they stop functioning like they're supposed to. That's oxidation.