Some types of air pollution might cause blood clots, says a new Harvard study. Researchers have found that the most dangerous form of air pollution is microscopic soot so small that it can be inhaled and will flow directly into the bloodstream. Once in the blood, these soot particles can wreak havoc, with clots forming around the particles. This syndrome, known as deep vein thrombosis, or DVT, is most common in bed-ridden hospital patients, sedentary people, and long-distance fliers. The clots can dislodge from the legs and travel to the heart, lungs, or brain, where they cause strokes or death. “We have known for some time that air pollution has been associated with increased risk of heart attack and stroke,” DVT expert Dr. Beverley Hunt tells “This study shows for the very first time that air pollution also increases the risk of clots in the veins and tells us why.”