TLDR L-cysteine slows down the breaking of bonds in hair due to electrostatic interactions.
The study investigated the reduction mechanism of L-cysteine (Cys) on keratin fibers in human hair using microspectrophotometry and Raman spectroscopy. It was found that Cys diffused into the hair in a non-Fickian manner, indicating electrostatic interactions between Cys's free amino groups and the anionic ions on the fiber surface. The disconnection of —SS— groups occurred at a slower rate than the diffusion of Cys, particularly at pH 9.0, suggesting that these electrostatic interactions decreased the reaction rate of Cys.
52 citations,
February 2005 in “Biopolymers” Chemical hair straightening changes hair proteins and mostly fixes broken bonds.
16 citations,
October 2003 in “Journal of applied polymer science” 2-iminothiorane hydrochloride improves hair waving permanence without damage.
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45 citations,
December 2006 in “Biopolymers” Permanent waving weakens hair by altering its protein structure.
October 2024 in “Cosmetics” ATG effectively reduces hair frizz without damaging hair strength.
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December 2012 in “PubMed” Permanent wave treatment with thioglycolic acid changes hair structure by altering disulfide bonds.
20 citations,
December 2012 in “Journal of molecular structure” The study found that thioglycolic acid breaks down hair bonds more consistently than l-cysteine, which is less damaging to hair.
January 2024 in “Molecules (Basel. Online)” Juglone from walnut extracts may help repair damaged hair.