Add another risk factor to the litany of health problems associated with fossil fuel emissions: blood clots.

We know that breathing smoggy air increases the risk of hearth disease and stroke, but researchers at the Harvard School of Public Health recently discovered that it can also trigger deep vein thrombosis — blood clots in the legs that travel up to the lungs and block the pulmonary artery.

To learn more about how blood travels through the body, including an interactive map of the circulatory system, visit Red Gold: The Epic Story of Blood online.