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Health answers: What are the health effects of ozone?

Q. What are the health effects of ozone?

A. Although ozone in the upper atmosphere protects us, near the ground it can harm. Ozone is produced as a byproduct of chemical reactions in sunlight; it’s a component of urban smog and its levels tend to be highest on hot, sunny days in cities.

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David Peden, an allergist and immunologist at the University of North Carolina at Chapel Hill, says that some people have an immediate reaction to ozone. They find it hard to take a deep breath, and may notice airway pain, irritation, cough, or wheezing. He says this seems to be a pain response and can be prevented or treated with pain relievers. Another effect is inflammation in the airways, which can aggravate asthma and allergy attacks, as well as other lung diseases. This effect is often delayed, Peden says, emerging 24 to 48 hours after ozone exposure. Research suggests that ozone may also impair heart function and cause more widespread inflammation in the body, and that chronic, long-term exposure may have lasting health effects, but the extent of these effects is still unclear.

Peden says that ozone exposure is determined by three factors: the levels in the air, how long you are exposed, and how hard you are breathing. For that reason, people should avoid vigorous exercise or long periods outdoors when ozone is high, particularly those with asthma or other respiratory problems. Ozone is one of five pollutants included in the Environmental Protection Agency’s Air Quality Index, found at

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