The patented 'bond-building' active in popular repair treatments. Hair does look and feel better; the claim that it rejoins broken bonds inside hair is unproven.
Bleaching and colouring break disulfide bonds, the cross-links that give hair strength. This ingredient, a maleate salt, is claimed to react with the broken ends and link them back together, and it is sold as a pre-treatment during bleaching and as an at-home mask, shampoo and conditioner.
Independent lab analysis of bleached hair treated with maleate-type repair agents found a smoother, more intact-looking surface but no increase in disulfide bonds and no direct sign of the claimed cross-linking.
Evidence consists mainly of manufacturer lab testing (breakage and strength measurements). An independent spectroscopy study of maleate-type repair agents found cosmetic surface improvement but no evidence of rebuilt bonds. There are no controlled trials on real-world breakage.
On bleached hair, maleate- and shikimic-acid-based repair agents changed the cuticle and cortex and made the surface smoother, but none increased disulfide bonds in the cortex, and nothing directly showed the claimed cross-linking reaction.