Molds are fungi that spoil bread, rot fruit, and mildew clothing. They also grow on dead leaves, grass, hay, straw, grains, and on other plants and in the soil. Since they are not killed by frost, the mold allergy season is long. Mold spores may be in the outside air year-round except when snow covers the ground.Indoors, molds grow on houseplants and in their soil. They also grow in damp places such as basements and laundry rooms. Molds can also be found in cheeses and fermented alcoholic beverages.