Soap scum is a common development in showers. It is a white, chalky residue that appears as a white or gray filmy layer. This can build up on all the surfaces in the shower, from the glass door to the walls, floor, and water handle. So how exactly does it form? Soap scum combines calcium and magnesium particles currently in the water with the soap, which develops into the soap scum substance. This formation is caused by minerals in tap water that combine with soap and dirt to create a layer of s