Mold and mildew are often used interchangeably, but they’re two different types of fungi. Mildew is usually white or grey, while mold is usually more colorful (green, blue, black, or yellow) with a fuzzy or slimy texture. Mildew grows on flat, already-wet surfaces, while mold often grows beneath surfaces. Because mildew is usually found on surfaces, it’s easier to clean and remove than mold. While both can cause allergic or respiratory issues, mold is a more severe health concern.