Mildew is a specific type of fungus with a powdery white or gray appearance, whereas mold is a fungus with a black and slimy or green and fuzzy. Mildew appears flat and doesn’t go deep, while a mold is raised, bumpy, and takes root. Both thrive in moist, humid conditions. Mildew can usually be removed with a household cleaner and soft scrub brush, while mold is often a stubborn stain that requires one of the techniques mentioned above.