The answer to 'upholstery mildew' is that mildew is a type of fungus that can grow on upholstered furniture, especially in damp or humid environments. Symptoms of upholstery mildew include discoloration, musty odors, and visible mold growth. Common causes include poor ventilation, high humidity, and water damage.
For minor cases of upholstery mildew, homeowners may be able to treat it themselves using a mild detergent or upholstery cleaner. However, for more severe or recurring mildew issues, it's best to call in a professional cleaning service. They have the specialized equipment and expertise to properly clean and disinfect the upholstery to remove the mildew and prevent future growth.