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

Objective: Following hair coloration with home or salon-applied hair dyes, sometimes it is desirable to have the option of removing this new colour and returning the hair to its natural appearance. This can either be immediately after coloration if the client does not like the colour, or it may be that a client wishes to 'reset' their hair and almost start again. There are oxidative and reductive methodologies to remove hair dye: (i) The oxidative method utilizes persulfate-based products, which are very difficult to control; however, professional hairdressers understand the limitations of what is possible without causing excessive oxidative damage to the hair fibre. (ii) The reductive method to remove dyes utilize sulfinate-based reducing agents commonly used in the textile industry. Commercial products based on these reducing agents have been, and are still being, used to 'decolour' dyed hair, albeit with significant drawbacks. The objective of this study was to introduce formamidine sulfinic acid and demonstrate its effective removal of hair dye in a safe and effective manner without the drawbacks of alternative reducing agents.

Methods: This paper describes and critically assesses the use, performance and drawbacks of ascorbic acid, sodium hydrosulfite, sodium hydroxymethanesulfinate (aka sodium oxymethylene sulfoxylate) and formamidine sulfinic acid as colour removal agents against different types and classes of hair dyes on human hair, and compares the various outcomes.

Results: The formamidine sulfinic acid system presented herein is an extremely effective reducing agent for use in removing colour from dyed hair. It works extremely well on all types and systems of colourants including permanent oxidative colourants (from different manufacturers) which represent the majority of products used in the hair coloration market.

Conclusion: 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.