Mildew is a thin, usually black, sometimes white, growth produced on many kinds of surfaces by molds.
Molds are simple plants belonging to the group known as fungi.
Though molds are always present in the air, those that cause mildew need moisture and certain temperatures in order to grow. They commonly develop in humid summer weather, especially in houses that are closed. They grow fastest at temperatures between 75 F. and 85 F. Sunlight helps kill mildew. These molds grow on anything from which they can get enough food. In homes they develop most often on cotton, linen, rayon, silk, wool, leather, wood, and paper.