Swelling During and After Treatment

Hair fibers that have been reduced and reoxidized approach the original fiber diameter. Indeed, Eckstrom [121] has suggested that the milder the conditions of reduction, the closer the fiber will return to its original dry-state diameter on neutralization. 

Fiber diameter determined in the wet or swollen state is sensitive to detect changes produced by damaging treatments like permanent waves or bleaches. The swelling action of permanent-waved hair [30] and in bleached fibers [32] is greater than in unaltered hair and has been used to estimate the relative extent of alteration produced by reduction and reoxidation [31]. For additional discussion on hair swelling, see Chapters 1 and 8. 

---