A Review of Permanent Waving and Perm Chemistry.

Although traditional perm chemistry has been around for over 70 years, it still arguably remains our best means of permanently altering the shape of hair. The hullabaloo created by the so-called Brazilian keratin treatments has led to resurgence in research activities in this area-and so an overview of the incumbent technology would seem pertinent. This review highlights underlying chemistry responsible for the success of traditional thioglycolate solutions but makes the case that our knowledge gap lies with the kinetics of the process. To this end, the merits and limitations of the single-fiber tensile kinetic approach are addressed-where, despite seemingly questionable assumptions, logical outcomes are obtained from systematic experiments intended to probe the validity of this method. Furthermore, results demonstrate how considerably different rates can arise between a common perm solution and hair from different sources. It is therefore proposed that "resistant" hair is a consequence of slow reaction rates which lead to an insufficient number of cystine disulfide bonds being broken during the processing time. Additional analysis of these kinetic data suggests the presence of different mathematical models that describe the progression of the process with varying experimental conditions. The reproducibility of results and the frequency with which models arise add confidence to findings.