How can I tell if I have black mold or mildew?

A mildewed surface is often difficult to distinguish from a dirty one. To test for mold and mildew and how to tell if your house has mold, simply dab a few drops of household bleach on the blackened area. If it lightens after one to two minutes, you have mildew. If the area remains dark, you probably have dirt.

Does mildew look black?

Mildew usually turns black or brown over time; Mold is usually fuzzy or slimy in appearance. It appears as irregularly shaped spots that can have different colors – blue, green, yellow, brown, gray, black, or white. Oftentimes, surfaces that are covered in mold begin to rot.