Mildew is a mass of white, gray or yellow hyphae, or fruiting structures, that grows on the surface of moist and warm areas like damp cloth, fibers, fabrics, paper, leather goods, and several plants. These fungi use these surfaces as mediums and sources of food for their growth and reproduction. This fungal growth is textured fluffy or powdery and often produces a distinctive smell. Floors, walls, ceilings, areas with lots of humidity, such as bathrooms, kitchens, and basements, may also contain mildew.

Although mildew is a type of mold, the word “mold” is usually used to describe mold that grows on food, while “mildew” tends to describe mold that grows on objects and surfaces.

Some mildew contains toxins called mycotoxins that can cause allergic reactions or illnesses in certain people.