Humidity Requirements for Mold Growth In the warm, humid areas of the United States and of the world, mold or mildew prevention ranks as a major pest-control problem. Leather goods, clothing, foods, mattresses, painted walls, and even glass camera lenses are subject to the unsightly appearance, stain, damage, or musty odor associated with the growth of the lowerorder plants belonging to the fungi and known popularly as mildew or mold.