Both mould and mildew are part of the “fungal” group of organisms. They both produce spores, and mycotoxins and allergyns. They are, obviously, very similar. IN GENERAL: mildew grows on living organisms: the mildew on flowers, powdery mildew on grass, etc. Most mould growth is on things that used to be alive. Mould grows on wood and paper and cardboard and wool and silk and leather, etc. Mildew grown on trees, shrubs and many living plants. What you see growing inside your home is probably some type of mould. All moulds must have something organic on which to grow. When you see mould growing on something that is not organic (concrete, plastic, glass) then it is actually growing on the DIRT that is on those materials. Dirt contains enough organic material to support mould growth.