"Mold" and "mildew" are terms that are used generally to describe growths of fungi on various surfaces. "Mildew" also is a scientific term that describes a type of plant disease. In common usage, the difference between mold and mildew usually is in their appearance and the surfaces on which they are growing. Mold is often thicker and black, green, red or blue in color, and mildew usually is lighter, powdery and gray or white. Both mold and mildew often grow in moist and warm locations, but mildew is more often found in showers, on paper and on fabrics, and mold is often found on foods and in walls and other permanent structures.
In plant science, the two main types of mildew are powdery and downy. Powdery mildew is commonly found on roses and other flowering plants, and usually looks like white or gray splotches. It is created by an ascomycota type of fungus. Downy mildew is from the oomycota type of fungus and is found in agricultural products such as grapes and potatoes. Its appearance varies from plant to plant, with some common indications being leaf spots and distortions, downy patches and crystalline spores that might look like sugar.
Around the house, mildew often forms in bathrooms, where moisture provides a suitable environment for fungi to grow. It also can form on objects, such as pieces of paper or clothes, that get damp and are left in one spot for several days or weeks. Mildew in these situations usually is a thin, powdery growth of fungus. When it is allowed to grow for a long period of time, it might turn into what most people would call mold.
Mold often looks fuzzy or slimy, depending on the type. A heavy mold might begin to look like a plant growth covering the surface. Some surfaces that are covered by mold might begin to rot. Mold can also appear in various colors. On a wall or ceiling, some types of mold might appear to be irregularly shaped spots of black or gray.
Some molds have toxins called mycotoxins that can cause an allergic reaction or other illness in some people. Symptoms of a mold allergy might include headaches, asthma and coughing. Irritation of the eyes and throat might also occur as a result of breathing mold toxins. Molds are not always harmful; the antibiotic penicillin was created from the mold of the same name.
Keeping areas dry is the most important preventative measure for eliminating mold and mildew. Moldy food should not be eaten. A mildew infestation on paper and some fabrics cannot be scrubbed off, but a mildew remover can usually get rid of mildew on harder surfaces such as those found in bathrooms. Some mold and mildew removal products should not be used by people who have asthma or in areas that are not well-ventilated. In situations where there is serious mold growth, a professional might be needed to clean the space and repair any damage.