Fungal (or mold) spores are commonly dispersed in air, and on some days 10,000 or more fungal spores can be found in a cubic meter of air. With every breath humans take, there is a high potential that fungal spores will be inhaled. Usually this is not a problem, but if the number of spores inhaled is high enough, susceptible and sensitized individuals may develop adverse effects, such as an allergic response. Recently it has been suggested that the spores of some fungi may contain toxins and that inhalation leads to deleterious effects when the toxins are released in the lungs. However, this conclusion is controversial.