Changing the Shape of Hair 182 Wong et al. published a key study on this topic in 1994.73 It is well known that reaction with alkali can convert disulfide bonds to lanthionine cross-links as illustrated in Figure 16.74,75 Because lanthionine formation accompanies relaxing, it had been presumed to be an important component of the relaxing mechanism. However, Wong et al.’s results work showed that this is not the case and that supercontraction is far more important to hair straightening than either lathionine formation, breaking of S-S bonds, or the ability of a treatment to swell the hair. Supercontraction is shortening of the fiber caused by conversion of α-helical proteins to the shorter random configuration and occurs when a wool fiber is permanently set in water at high temperature.76-78 Wong et al. investigated the effects of several different treatments on hair straightening, lanthionine formation, S-S bonds, and swelling. Treatments included NaOH, lithium chloride (LiCl), ammonium thioglycolate (ATG), resorcinol, and boiling water. Table 3 summarizes some of that study’s key results. Table 3 Effects of treatments on S-S bonds, lanthionine formation, supercontraction, and hair straightening data summarized from Tables I and II from Wong et al.73 Treatment pH (S-S) %Lanformed %Super Contraction Degree of Straightening NaOH (1N) 14.0 -35 5.7 24 Complete/Permanent NaOH (0.1N) 13 -30 17 0 Partial/Temporary TGA (ATG) 9.6 -45 0 0 Partial/Temporary LiCl (40%) 7.0 3 0 11.5 Complete/Permanent Resorcinol (40%) 7.0 _ 0 10 Complete/Permanent Boiling Water 5 0 6 Complete/Permanent Lithium chloride, resorcinol, and boiling water were all able to produce permanent straightening without forming lanthionine Figure 16 Schematic illustration of lanthionine formation