PERMANENT WAVING AND PERM CHEMISTRY 129 j 2 3 3 K - S - S - K Na SO K - S - SO Na NaS - K (22) T he a ttraction of sulfi te/bisulfi te as an active relates to the ability to reverse the aforemen- tioned reaction by rinsing with water and therefore essentially making it a one-step treatment. However, these treatments are not able to create tight well-defi ned curls and are mostly found as weak body waves. Sensitization issues associated with sulfi tes may also be a concern. EVALU ATION OF WAVE EFFICACY In th e salon, the effi cacy of a perm treatment is judged by a visual assessment of the curl shape relative to the size of the waving rods. A close relationship between the resulting curl and the rod diameter is often termed “true to rod” performance. However, based on previous discussions, it is evident that any evaluation of perming performance should also involve some durability assessment, possibly after exposing the hair to adverse conditions that are nonetheless in line with everyday occurrences (e.g., repeated shampooing and/or exposure to elevated humidity). A mor e precise method is often desired in the laboratory that allows for quantifi cation of both the initial and long-lasting effi cacy. A method that remains popular involves adapta- tions of an approach fi rst described by Kirby (40). The testing process involved setting the hair shape by wrapping tresses or bundles of fi bers around the pins on a pegboard. Figure 23 shows an example of such a utensil. (Note: a modifi cation of this approach has been adopted in the hair spray category, where it is also used to quantify style retention and longevity.) Once anchored, the hair can then be treated with an appropriate dosage of Figure 23. Pegboard for use in Kirby wave effi ciency testing.

JOURNAL OF COSMETIC SCIENCE 130 perm solution, which is left on the hair for a suitable duration. The hair can then be rinsed and towel blotted before application of the neutralizing solution. The process fi n- ishes with one last rinse and drying of the hair. All manipulation can be performed with the hair anchored on the pegboards. The waving effi ciency can be expressed as percentage by comparing the length of the treated hair (Ltreated) with the initial tress length (Lo) and that of the “perfect wave” as dictated by the dimension of the pegboard (Lf), t ha t is, d d ¯ q100 ¢ ± treated Percentagewavingefficiency 1 L L L L (23) Sim ilarly, the longevity of the treatment can be assessed as a function of time (or other external stimuli) by equation (24), th at is, d d ¯ q100, ¢ ± treated 0 Percentagewavingefficiency 1 L L L L (24) wher e Lt is the tress length after the appropriate stimuli. SUMM ARY It i s possible to fi nd reviews and summaries pertaining to the topic of perm chemistry, which perhaps presents the impression that this area is well-understood. Accordingly, this overview attempts to take a somewhat different stance, by dedicating a signifi cant portion to what we still do not know about the process (perhaps in the hope that others will take up the cause). It is suggested that the underlying chemistry is relatively straightforward and can be found in any elementary textbook. But, before reactions can occur, it is necessary for reactants to come together, and to this end, it is surprising that so little is known about penetration routes and rates of diffusion into hair. It has been hypothesized that variability in diffusion rates could be a cause of differing activity between a common perm solution and hair obtained from a diverse population. Results shown herein indicate signifi cant differences in both rates and kinetic mechanisms as a function of hair type, and it appears reasonable to suppose that “perm- resistant hair” is a consequence of relatively slow bond cleavage that produces an insuffi cient degree of transformation during treatment time. However, an explanation for these differences in diffusion rates (and indeed a means of measuring this property) requires further work. Addressing this point seems crucial in producing any enduring makeover (perm chemistry or not) because transformation will likely require penetration of “actives” into the hair. Afte r all this time, it is rather remarkable that perm chemistry still likely represents the best available means for permanently changing the shape of hair. The hullaballoo created by the so-called Brazilian keratin treatments in recent years has reignited research interest in this area, but there is no immediate indication of a safe, effective substitute for perm chem- istry. Although not wanting to stifl e new ideas, it is obviously prudent to ensure that every- thing has been squeezed out of existing technologies before moving on to new areas, and it is again noted that perm products have changed very little since their inception in the 1940s. Research efforts since this time have primarily focused on alternative actives (although still predominantly thiols), yet incumbent thioglycolate-based products still overwhelmingly dominate the shelves. It is worth re-examining why this material has been so diffi cult to