Super mild oxidation coloring: preventing hair damage at the molecular level

Citation: IFSCC Magazine, 10 (2007) (4) 323–329 Hydrogen peroxide is widely used for oxidation hair coloring or bleaching. It displays a high redox potential and easily penetrates into the hair fiber. This renders hydrogen peroxide capable of non-specific interactions with cortex and cuticle proteins resulting in irreversible cleavage of cystine crosslinks. Various classes of antioxidants were screened for their anti-hair damage effect in a permanent hair dye formulation using NIR spectroscopy. In parallel, the effect on the coloring and lightening performance was studied to exclude unwanted side effects on primary product performance. The screening criteria were fulfilled by organic disulfides such as α-lipoic acid but interestingly not by powerful antioxidants such as tocoperol, dibutylhydroxytoluene, or beta-carotene. Alpha-lipoic acid significantly protected human hair during oxidation coloring as demonstrated by (i) amino acid and protein analysis, (ii) surface polarity measurement, (iii) lipid analysis, (iv) differential scanning calorimetry, and (v) combing work measurement. Our results show that radical scavenging properties alone do not render antioxidants suitable for hair protection during oxidative treatments. The presence of disulfide bonds appears to be very favorable and it is likely that the intramolecular cross-link within α-lipoic acid provides a kinetically controlled protection for cystine crosslinks during oxidation coloring. Keywords: alpha-lipoic acid, antioxidant, hair damage, hair dye, NIR spectroscopy Paper presented at the IFSCC Conference 2007, Amsterdam, The Netherlands