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Is the acid working as an oxidizer or reducer with the melanin of the hair breaking down the bonds?

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Hair is mainly keratin, the same protein found in skin and fingernails. The natural color of hair depends on the ratio and quantities of two other proteins, eumelanin, and phaeomelanin. Eumelanin is responsible for brown to black hair shades while phaeomelanin is responsible for golden blond, ginger, and red colors. The absence of either type of melanin produces white/gray hair.

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I think the citric acid (in lemon) acts as a bleaching agent. The "bleach" reacts with the melanin in hair, removing the colour in an irreversible chemical reaction. The bleach oxidises the melanin molecule.

The illustration of the molecules perhaps might give a better picture on which groups are oxidised in the process.

The melanin is still present, but the oxidised molecule is colourless. However, bleached hair tends to have a pale yellow tint. It behaves as an oxidising agent at least according to my findings.

Acknowledgements

  1. https://www.thoughtco.com/salon-hair-color-chemistry-602183

  2. http://www.keratin.com/as/as002.shtml

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  • $\begingroup$ Lemon juice is rather a reducing than an oxidizing agent. $\endgroup$ – aventurin May 28 '17 at 19:21
  • $\begingroup$ @ave Is it? Because for the particular reaction to work it behaves as as weakly oxidising agent. I'm quite aware citric acid is a better reducing agent in most of reactions, but if that the case in this "bleaching reaction" I stand corrected, in research though I couldn't get substantive evidence to support that theory. $\endgroup$ – xavier_fakerat May 28 '17 at 19:26
  • $\begingroup$ Lemon juice contains citric acid and ascorbic acid. Both are used as antioxidants in the food industry. I doubt that citric acid could oxidize anything but strong reducing agents. I also have serious doubts about the hair lighting power of lemon juice (pure, no light, etc) in a scientific experiment. ;-) $\endgroup$ – aventurin May 29 '17 at 16:46
  • $\begingroup$ Yes I agree with with, actually this works with powerful oxidising agents like hydrogen peroxide, however this reaction some argue that it works but the hair has to be exposed long enough in sunlight, but haven't tried I just did a bit of research and put my findings in the answer above. $\endgroup$ – xavier_fakerat May 29 '17 at 17:54

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