Here's why:

* Ozone is a powerful oxidant: This means it readily reacts with other molecules, causing damage. When inhaled, it can damage lung tissue, leading to:

* Inflammation: Causes coughing, wheezing, and shortness of breath.

* Reduced lung function: Makes it harder to breathe.

* Increased susceptibility to respiratory infections: Makes you more likely to get sick.

It's important to note that ozone in the stratosphere (the ozone layer) is actually beneficial, as it protects us from harmful UV radiation from the sun. However, ozone near the surface is a pollutant and harmful to human health.