Hardened toilet stains are urine scale and need an acidic cleaner
#0031 Home & daily life
Fact rank
A
Confirmed in material from two sanitary-ware makers and a cleaner manufacturer
Wow rank
A
The surprise that the stain is a kind of stone
Usefulness
A
A clear use when choosing a toilet cleaner
Verification: Supported by evidence
AI verification reports the evidence it found; it does not guarantee that a claim is true.
Hardened yellow stains stuck to a toilet bowl are urine scale, removed by dissolving with an acidic toilet cleaner. Everyday dirt comes off with neutral detergent, but hardened urine scale does not come off easily with it.
Why
Urine scale is calcium from urine that has hardened, and acid dissolves it.Evidence
Primary LIXIL FAQ (urinals): urine scale is hardened calcium from urine and is removed with a commercial (acidic) urine-scale remover link
Primary TOTO care instructions: routine cleaning is done with neutral toilet detergent on a toilet brush link
Notes and limits
Mixing chlorine-based and acidic toilet cleaners, or using one right after the other, releases toxic chlorine gas. Urine scale is sometimes called "alkaline grime", but a 2021 paper in the Journal of Home Economics of Japan calls that description inappropriate for poorly water-soluble grime. Citric acid can also be used, though it has been noted to leave insoluble deposits easily. Some cleaners cannot be used on certain bowl materials or coatings, so follow the manufacturer's guidance.
Derivations
Derived from: 汚れと洗剤は相性で選ぶ
Derived facts: —