Stainless steel soap

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A stainless steel soap is a piece of stainless steel, usually in the shape of a soap bar. Its purpose is to neutralize or reduce strong odours from the hands, present from handling odorous ingredients such as garlic, onion or fish.^[1] The shape of a soap bar is purely decorative and any piece of stainless steel, such as a spoon, can be used for the same purpose.

There are similar applications, such as stainless steel disks in shoes and dishwashers, that are used to absorb odors. ^[2]

In the absence of plausible chemical explanations of why this may work, or experiments using controls, it is unknown whether the stainless steel soap is actually effective. Stainless steel soaps are often advertised for use with water; so it is likely that sulfurous compounds either dissolve directly in the water or are catalyzed by the steel, if indeed the odour removal is measurably greater with stainless steel than any other substance.

Stainless steel consists of mainly iron and chromium, and contains a thin layer of chromium (III) oxide on its surface. Metal oxides are Lewis acids and readily catalyze oxidations. Iron and chromium oxides can be used as oxidation catalysts, effective for industrial-scale oxidation of odorous reduced sulfur compounds at a temperature of 180 C.^[3] Another plausible explanation is that a thin layer of grease, containing the odorous compounds, is rubbed off mechanically onto the steel surface. Chromium(III) may also act as an adsorbent.