Mold come from a family of organisms that are found throughout nature, along with pollens from trees, grasses, and weeds, and are an important cause of seasonal allergic rhinitis. Allergic rhinitis is stimulated when microscopic fungal spores or, sometimes, fragments of fungi are inhaled. Because they are so small, mold spores may evade the protective mechanisms of the nose and upper respiratory tract to reach the lungs.
Mold grow in units called mycelium and reproduce through the formation of spores. Spores frequently become airborne, and like pollen, can cause allergic disease.
Mold is popularly associated with human disease because it is fungus. People can develop fungal infections of various types, especially those with poorly functioning immune systems. Fungi are also known to produce toxins, which are the major causes of various diseases.
According to Doctor Daniel More, molds can also cause severe immune reactions as a result of colonizing (living in, but not causing an actual infection) the lungs (hypersensitivity pneumonitis) and the sinuses. Molds are also well known to cause various allergic diseases, such as allergic rhinitis and allergic asthma.
People allergic to molds may have symptoms from spring to late fall. The mold season often peaks from July to late summer. Unlike pollens, molds may persist after the first killing frost. Some can grow at subfreezing temperatures, but most become dormant. Snow cover lowers the outdoor mold count dramatically but does not kill molds. After the spring thaw, molds thrive on the vegetation that has been killed by the winter cold.