Every summer the smog warnings return, but what does it really mean for your health? Smog, that sometimes brownish grey fog made up of fine particulate matter and ground-level ozone, as well as chemicals like VOCs and sulphur dioxide, is known for aggravating existing lung conditions and even causing new harm to your lungs. While the ozone layer found in the stratosphere helps protect us from UV rays, ozone molecules closer to the ground can irritate the respiratory system. That ground-level ozone is caused by things like vehicle exhaust and other pollutants reacting with sunlight, and it’s further amplified by extreme heat, which can prevent plants from absorbing the pollution they usually remove from the air. That’s why smog is often found in cities in the summertime. Some studies have found that every major urban centre in Canada has enough ozone to cause harm to your lungs. And while we don’t have it as bad as much of the world (the World Health Organization says of the nearly four million deaths caused by outdoor air pollution in 2012, about 90 percent were in the developing world), there is still reason for concern. The tiny particles found in smog can become trapped in your lungs, causing long-term damage, while the ozone that enters your lungs can harm the lining and cause inflammation. Smog can cause some people to experience shortness of breath, coughing, worsened symptoms of asthma and COPD, as well as fatigue. As a form of air pollution, smog is also considered a carcinogen, and new research shows that smog-filled days increase the risk of heart attacks and other serious health problems. While the link between heart disease and air pollution is yet to be fully explained, there is good reason to believe that you need to pay attention to the air you breathe in order to keep your heart healthy. One study has shown that as many as 6,000 premature deaths in major Canadian cities each year are due to smog. Want to reduce your risk? Check out your air quality forecast and take these steps to keep your heart and lungs safe: -If it’s a high-smog day, stay indoors. It’s not worth the risk. -Switch your outdoor workout to late in the day, when it’s cooled down a bit, or move it indoors. The more strenuous the activity is that you’re doing outside, the more harm the smog can cause you. -Avoid contributing to smog by ensuring you don’t idle your car, use harsh paints or cleaners, or use a gas-powered mower on extremely hot days. Avoid driving whenever you can to limit exhaust fumes. -Don’t drive with your windows down. A U.S. study found that it’s better to recirculate the air in your car than to suck in all the traffic-exhaust-filled air from the highway around you. -And don’t forget to check in on neighbours or family members, especially active kids, seniors or people with existing lung conditions. Many people still don’t appreciate the dangers of smog and may take unnecessary risks on sweltering summer days. (Photography: WikiCommons/BriYYZ)