In addition to having a bad odor, high concentrations of sulfur dioxide can affect breathing, cause respiratory illnesses and aggravate existing respiratory and cardiovascular diseases. Because of its solubility, SO2 is almost entirely removed from the mouth, throat, and nose through breathing. Therefore, the principal effect of SO2 is to alter the mechanical function of the upper respiratory system. Exposure to SO2 at very low levels (0.25 - 0.5 ppm) can cause bronchitis, and at concentrations lower than 6 ppm can irritate the lungs and throat. A long period of exposure to concentrations above 6 ppm impairs the respiratory system's defenses against bacteria and foreign particles.
The health consequences of sulfur dioxide are more serious when combined with particulate matter and ozone. Since SO2 and particulate matter may come from a common source, such as the combustion of coal, high SO2 levels are often associated with high particulate-matter levels.
Populations most susceptible to the effects of SO2 are children, the elderly, asthmatics and those with chronic lung disease such as bronchitis and emphysema.