Soap scum

In detail

Soap scum is a chemical product of the water rather than a soiling of the surface. Soap is a sodium salt of a fatty acid; hard water carries dissolved calcium and magnesium; and when the two meet, those metals displace the sodium and produce calcium and magnesium salts of the same fatty acids. Those salts are not soluble in water, so they come out of solution as a curd which then dries onto glass, tiles, taps and the bath. That single reaction explains almost everything readers find puzzling about it. It appears in hard-water areas and not in soft ones. It appears with bar soap far more than with body wash, because synthetic detergents were developed precisely so their heads would not precipitate with hardness ions. And it resists both of the obvious treatments used alone: a descaler attacks the mineral half and leaves a greasy film, while a detergent attacks the fatty half and leaves a mineral haze. The deposit is a hybrid and usually needs an acidic cleaner and a surfactant together, or one then the other with a rinse between. Prevention is more effective than any product, because the film needs the water to evaporate in place in order to deposit at all.

Why

• Soap scum is explained by Insoluble metal soaps
• Soap scum is explained by Water hardness
• Soap scum is explained by Evaporative deposition
• Soap scum is explained by Adhesion and cohesion
• Soap scum is explained by Why different surfaces get different dirt

Aftercare and prevention

• Squeegee helps prevent Soap scum
• Moisture control helps prevent Soap scum

Hacks and claims involving this

• One spray for the whole bathroom Does not work