PERMANENT WAVING AND PERM CHEMISTRY 127 mon to encounter claims pertaining to an active or formula being “less damaging” but these treatments are also milder and consequently also less effective. By means of illustra- tion and continuing with the earlier example, the positioning of a cysteamine-based product as a “less-damaging” perm may be technically correct, but at the same time, it is not a true comparison as levels of transformation are unlikely to be equivalent. It should be remembered that one can also move up and down this damage-effi cacy trade-off curve by the way these products are used, namely, increased effi cacy, but also greater damage, can result from higher product dosages and longer exposure times. With all this said, there are other means by which the hair structure can be damaged that lead to other consumer-related issues. A few articles describe extreme levels of swelling when treating hair with thioglycolate and other reducing agents. Valko and Barnett (32) and Powers and Barnett (33) reported swelling of up to 300% after prolonged soaking in a thioglycolate solution. This occurrence reverses during the oxidation process as bonds are reformed (34) although Shansky (35) noted additional swelling during the rinsing step between the reduction and oxidation steps which he attributed to osmotic forces. This ballooning of dimensions would seem to impose considerable strain on the outer struc- ture of hair, whereby uplifting, cracking, and general deterioration of cuticle scales may be anticipated. The condition of this outer surface is the major contributor to the tactile properties of the hair, and its deterioration will be refl ected in a variety of consumer- related terms. Perhaps most notably, a rough, course hair feel is often described by consumers as “dryness,” although technical measures indicate no decrease in water con- tent (30,36). The aforementioned swelling properties of hair are permanently altered by these treat- ments whereby increased dimension changes arise during immersion in water. This has led some to suggest that this property can also be used as one measure of damage (37,38), but the consequences of this altered state are perhaps more interesting and important. One of the most notable repercussions of these treatments involves the considerable increase in wet-state grooming forces. The popular explanation for this occurrence generally involves a degrading cuticle structure but in this author’s experience, scanning electron micros- copy images do not usually show an especially damaged surface in freshly permed hair. Instead, it is believed that enhanced swelling produces a marked increase in the wet hair volume which subsequently results in higher grooming forces. An increased predilection for swelling is also widely believed to impact diffusion rates for materials both in and out of the hair. This represents a likely explanation for the especially fast transformation rates that arose during SFTK experiments on bleached hair. ADAPTATIONS WITHIN THE PERM PROCESS Several perm variants can be found on the beauty aisle shelves. Most fall within a classifi - cation termed alkali waves because of their basic pH (generally 8–9.5) for the reasons described earlier. There is also an acid perm category, although technically the name is a misnomer as these products are also basic in composition (generally pH 7.5–8.5), but not as alkaline as the previous category. This positioning generally equates to propositions involving reduced hair damage, where more caustic conditions may be anticipated to compromise hair to a greater extent. There is some truth to this idea, although there are complicating factors that preclude such a simple statement. High-pH conditions can lead to increased fi ber swelling and
JOURNAL OF COSMETIC SCIENCE 128 hydrolysis of the hair protein, although the literature suggests that these occurrences predominantly occur under more extreme conditions than those used in perms. However, as described previously, the concentration of the active thiolate ion is dictated by the value of the pH relative to the pKa of the thiol. Therefore, acid perms use less aggressive reaction concentrations and therefore sit toward the lower end of a damage–effi cacy trade- off curve. In addition, acid perms often use glycerol monothioglycolate as an active, and it can be further speculated that reduced effi cacy may also be a consequence of this larger molecule diffusing more slowly into the hair. As described earlier, it is common to see DTG being added to thioglycolate-based perms to limit the progression of the second equilibrium reaction see equation (9). To chemists, this represents a fortuitous practical demonstration of Le Chatelier’s princi- ple however, in the creative minds of product marketers, these formulations become self-timing perms. Salce et al. (10) generated results that showed this expected behavior on introducing the oxidized dimer into formulations, but Manuszak et al. (21) were not able to observe any effect in SFTK experiments. It is possible that the high solution-to- hair ratio in SFTK experiments prevents the buildup of suffi cient concentrations of this reaction product. Yet another variant involves exothermic perms which represent a modern adaption of the machineless waves that were described in the Introduction section. These treatments in- volve mixing two solutions before application. The fi rst generally contains a somewhat higher concentration of thioglycolate, and the second has a relatively low level of hydro- gen peroxide. Therefore, on mixing, the two reagents undergo reaction with a signifi cant release of heat, while still providing suffi cient thioglycolate concentration for reaction with the hair. In addition, this reaction produces DTG whose signifi cance has been high- lighted. Outside of damage, the other major issue with conventional perm products involves the smell. There are two primary contributors to this issue: (i) the odorous nature of thiols themselves and (ii) the smell of ammonia, which is commonly used as a pH adjustor. Although unpleasant, these smells will only persist for a short time after treatment and will gradually dissipate after a few days. However, a curious alterna- tive issue can arise when using cysteamine-based perms. These products were intro- duced into the U.S. market as low-odor perms because of the less noxious smell of the active relative to thioglycolate. However, an unexpected occurrence involved the development of a new odor, often likened to “wet dogs,” that arose within a few days to a week of usage. It has been suggested that this new smell is due to the formation of alkyl thiazolidines (39) which are produced when residual cysteamine (tied up within the hair as mixed disulfi de) is gradually released and reacts with sebaceous components. The only commercial exception to the thiol classifi cation of perm actives involves sulfi tes, SO32- (or at low pH, bisulfi tes, HSO3-). These too are reducing agents, and equation (21) shows the half equation for the oxidation of sulphite to sulphate under alkali conditions. j 2 2 3 4 2 SO 2OH SO H O 2e (2 1) Mean while, equation (22) shows the reaction scheme for sodium sulfi te attacking the keratin disulfi de bond with the formation of the so-called bunte salt (i.e., K-S-SO3Na).
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