Although there are many types of molds, only a few dozen cause allergic reactions. Many molds grow on rotting logs and fallen leaves, in compost piles and on grasses and grains. Unlike pollens, molds do not die with the first killing frost. Most outdoor molds become inactive during the winter. In the spring they grow on plants killed by the cold. Indoors, fungi grow in damp areas. They can often be found in the bathroom, kitchen or basement.
Inhaling the spores causes allergic reactions in some people. Allergic symptoms from fungus spores are most common from July to early fall. But fungi grow in many places, both indoors and outside, so allergic reactions can occur year round.
Mold spores get into your nose and cause hay fever symptoms. They also can reach the lungs and trigger asthma. A chemical released by allergy cells in the nose and or lungs causes the symptoms. Sometimes the reaction happens right away. Sometimes a mold allergy can cause delayed symptoms, leading to nasal congestion or worsening asthma over time. Symptoms often get worse in a damp or moldy room like a basement. This may mean you have a mold allergy.