According to the Centers for Disease Control (CDC) six varieties of mold are common and three can produce toxins harmful to humans. Spores easily spread through the air, acting like seeds forming new colonies under the right conditions. They act as irritants and can produce such symptoms as sneezing, watery eyes, nasal stuffiness and other similar allergic reactions. Individuals sensitive to mold may also experience fever, shortness of breath and wheezing. Some people with chronic illnesses such as obstructive lung diseases may develop mold infections in their lungs.