Role of Redox Metals in Color Formation in a Hair Colorant.

The objective of this work was to identify if low levels of redox metals such as copper would accelerate color formation on hair and to understand the consequent impact on initial color formation and color fade. Kinetics of color formation with oxidative dyes in solution in the presence of varying concentrations of copper ions were assessed via imaging and color measurements. Color uptake on hair and color fade were measured with a spectrophotometer, and copper levels in hair were measured with inductively coupled plasma atomic spectroscopy after hair digestion. In this work, the role of redox metal ions such as copper and iron on accelerating rates of oxidative dye formation was demonstrated. Kinetics of dye formation were measured in solution for three dye couples-p-phenylene diamine (PPD) plus resorcinol, PPD plus 5-amino-2-methylphenol (AHT), and 4,5-diamino-1-(2-hydroxyethyl) pyrazole sulfate (HDAP) plus AHT- in a solution that also contained ammonium hydroxide and hydrogen peroxide at pH 10. Low levels of copper were added at a concentration range from 0.01 μg/g to 0.1 μg/g and the rate of color formation measured over 2 h. All th ree dye couples showed signifi cant color acceleration that increased with increasing levels of copper. A mechanism where initial oxidation of primary intermediate PPD or HDAP is accelerated is proposed. This mechanism is demonstrated to become important when trace levels of copper are in hair and a hair colorant added. Color formation is accelerated outside versus inside hair, and ultimately, color uptake is reduced after the colorant is rinsed off hair. Noticeable color fade versus the starting hair color is also increased. This work provides evidence for the role of copper ions in color formation in hair and strategies to reduce copper levels in hair using a chelant such as histidine in a shampoo or conditioner before coloring.

Citation

Jennifer M Marsh, Robie L Lucas, Chris Cowans, Shane Whitaker. Role of Redox Metals in Color Formation in a Hair Colorant. Journal of cosmetic science. 2021 May-Jun;72(3):268-278

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PMID: 35361315

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