While they are the same gas, ozone in the upper atmosphere is essential to life because it filters ultraviolet radiation from the sun. Conditions that lead to ozone formation tend to become most severe during the months of May through October when the weather is hot and sunny with relatively light winds. You can't see ozone, smell it, touch it, or reach out and grab it. Even though ozone is a colorless gas, that doesn't mean it's harmless. Ozone can limit the ability to take a deep breath, and it can cause coughing, throat irritation, and breathing discomfort.
Ozone can increase the susceptibility of the lungs to allergens and other air pollutants.
Children and those with pre-existing lung problems are sensitive to the health effects of ozone because breathing ozone can affect lung function and worsen asthma attacks. Healthy adults involved in moderate or strenuous outdoor activities can experience the unhealthy effects of ozone. Even at relatively low levels, ozone may cause inflammation and irritation of the respiratory tract, particularly during physical activity. The resulting symptoms can include breathing difficulty, coughing, and throat irritation. In order to qualify as an ozone attainment area, a region may not exceed maximum air pollution levels on more than three days during any three-year monitoring period.