Removal of synthetic hair dye using formamidine sulfinic acid and other sulfinate precursors

The colour removal effectiveness of sodium hydroxymethanesulfinate (sodium oxymethylene sulfoxylate) is good, but it has three drawbacks: (i) it produces formaldehyde, (ii) the colour can return and (iii) can result in unpredictable shades on subsequent oxidative colouring. The formamidine sulfinic acid system presented herein is extremely effective and gives excellent colour removal results across different colourant systems with the added benefit that it does not have the drawbacks that the other systems have.