Chapter 5 183 while 0.1N NaOH did form lanthionine without yielding permanent straightening. Straightening ability was correlated supercontraction and not with lanthionine formation or with the percent of S-S bonds broken. Ogawa et al.52 reported a curing method for straightening hair using ammonium thioglycolic acid (AGT) and dithiodiglycolic acid (DTDG) and heat. These authors also found that permanent straightening correlated with supercontraction. The AGT/DTDG/ heat treatment causes supercontraction but is at too low a pH to cause lanthionine formation. High pressure differential scanning calorimetry was used to investigate the reduction of α-helical protein. A strong correlation was found between reduction of the enthalpy α-helical proteins and hair straightening efficacy. The most thorough study on hair straightening/relaxing this author is aware of is the PhD thesis of Dr. Jutta Quadfleig.79 At the time of this writing, the work does not appear in the literature, but the thesis document can be downloaded.89 Both lye and no lye relaxers were studied alone and in combination with permanent waves. Straightening effect was measured quantitatively from changes in hair length. Measurements of straightening rate, lathanonine formation, supercontraction, and keratin denaturation enthalpy all led to general agreement with the hypothesis that lanthionine formation is a side reaction of the relaxation process and does not contribute directly to the mechanism. Again, disordering of α-helical proteins leading to supercontraction seems to be the most important variable for predicting straightening efficacy. It appears that the hypothesis of Wong et al., that supercontraction is the most important factor in relaxing excessively curly hair, has been well supported by subsequent research findings. Hair Damage by Relaxers Relaxers are certainly among the most damaging treatments to which consumers subject their hair. Hair of African origin is already weaker than Caucasian or Asian hair and relaxing may reduce the breaking strength by as much as 50%.80,81 For an example of the