Repeatable Perming via Thiol–Michael Click Reaction: Using Amide Derived from Maleic Acid and Cystine

This study introduces a novel thiol-Michael click perming molecule, N,N'-bis(maleoyl)-l-cystine (MA2-CySS), which enables repeatable perming without oxidative damage. The molecule was synthesized and shown to be non-cytotoxic up to 1000 μg/mL. The perming efficiency of MA2-CySS was comparable to traditional oxidative methods, achieving over 1300% efficiency across three cycles, while significantly reducing color change and cuticle damage. It also preserved hair keratin's secondary structure better, maintaining higher α-helix content and disulfide bond retention. This represents a significant advancement in perming technology, offering a less damaging alternative to conventional methods.