Chemistry
Same chlorine family, different pH
A side-by-side look at the usual pH of household bleach and of HOCl-type solutions, and what that does to the HOCl / OCl⁻ split.
It is easy to assume that a lower-ppm solution must be easier on metal. The studies collected for this site do not support that assumption.
Side by side
| HOCl | Bleach | |
|---|---|---|
| Steel knives, repeated exposure (Bryant 2026) | A 200 ppm product, used neat, produced the most rust of all products tested. | 7,500 and 30,000 ppm dilutions also corroded the knives, but less. |
| Carbon-steel dental burs (Kameda 2022) | Rusted more than with alcohol. | Rusted more than with alcohol. |
| Effect of pH | Within HOCl-type solutions, a strong-acid type was the worst for precious dental alloys and a neutral type the least (Dong 2003). | Sil 2025 notes that neutral or low pH increases hypochlorite’s corrosiveness. |
| Concentration | — | CDC lists hypochlorites as corrosive to metals at high concentrations, above 500 ppm (CDC 2008, p. 41). |
Reading the knife test
Bryant 2026 exposed steel boning knives to several oxidizing products over repeated cycles. The authors report that “knives exposed to hypochlorous acid exhibited the most substantial corrosion (rust).” The HOCl product was at about 200 ppm; the bleach dilutions were at roughly 37 and 150 times that. One test on one kind of steel is not the last word, but it is enough to rule out any general claim that HOCl spares metal.
Why pH shows up again
Lower pH tended to raise corrosion in these sources: Sil 2025 notes it for bleach, and in Dong 2003 strong-acid electrolyzed water was the worst for precious dental alloys, though a cobalt-chromium alloy held up better in it. That is the same pH thread that runs through Same chlorine family, different pH. CDC also records that one endoscope maker voided its warranty when superoxidized water was used on its equipment (CDC 2008, p. 41). Check the equipment maker’s guidance for either solution.
For the broader comparison, see HOCl vs bleach on disinfectant.org.
Sources: Bryant 2026 (PMID 42347257); Kameda 2022 (PMID 34690228); Dong 2003 (PMID 15005226); Sil 2025 (PMID 40021972); CDC 2008, p. 41. Full entries on Sources.