Mould is found in badly cleaned refrigerators on foods and in all damp corners of the house on the wallpaper and in bathrooms. Mould is also found outdoors. For example, the fungus Cladosporium herbarum grows on grass and cereals as well as in greenhouses.
Mould consists of a network of microscopically small threads and produces spores. As with the pollen count in plants, fungus has a spore count. Both spores and fragments of fungus are transported through the air into our respiratory tracts, where they release substances which can cause an allergic reaction in people who suffer from mould allergy.