Exposure to mold can occur when airborne mold particles, mostly spores and fragments, are inhaled. We breathe in mold spores and fragments every day, indoors and out. Usually these exposures do not present a health risk. However, health problems may result when people are exposed to large amounts of mold, particularly indoors. Inhaling excessive quantities of airborne mold particles, fragments or spores may lead to allergic illness, trigger asthma, cause respiratory infections, or may bring about toxic effects from certain chemicals in the mold cells. Following are descriptions of health problems that can be caused by exposure to mold.