Damage to African hair is exacerbated after it has been chemically straightened with alkaline relaxers. This process, among other negative effects, causes breakage of disulfide bonds and protein losses that weaken the whole hair structure, leading to a reduction of its resistance to break. African hair is, thus, more fragile after the straightening process. Yet, everyday grooming practices require it to be subjected to other damaging practices such as blow drying and hot ironing. As a result, the hair is further damaged, making it dull, weaker and more difficult to style.
For these reasons, straightened African hair needs products that outperform those used in other types of hair; products that not only protect the hair against thermal or mechanical damage, but also, restructure, re-fat, moisturize, condition and consequently facilitate styling. Unfortunately, there is a lack of ethnic hair care products that can provide this multifunctional level of performance. Thus, people with relaxed hair, so far, have tried to minimize damage and condition their hair by applying large doses of heavy and oily products.
Fig. 1: SEM micrograph showing a typical African hair fiber.
Blow dryers and hot irons cause thermal damage to African hair. African hair in its virgin state has more cystine bonds on its surface than any other type of hair,1 yet when it is subjected to cycles of wetting and blow-drying it undergoes similar patterns of thermal damage. Although, we have found that for virgin fibers of the same diameter the average number of cracks formed in African hair is lesser than in Caucasian hair (Fig. 2). Furthermore, the experimental evaluations appear to indicate that virgin African hair is slightly more resistant than Caucasian hair to the phenomena of cuticle cell lifting produced by hot irons. This situation, however, reverses after African hair has been chemically relaxed; i.e., its susceptibility to thermal damage either with blow dryers or hot irons increases substantially (Fig. 2).
Fig. 2: Counts of lifted cuticle cells and thermal cracks produced in virgin African, Caucasian, and relaxed African hair, as described in reference 4.
Fig. 3: SEM micrograph of relaxed African hair with thermal cracks produced by 25 cycles of wetting and blow drying according to method described in reference 4.
Luviquat Sensation is another product from BASF Care Chemicals that can be used for thermal protection. It is a cationic conditioning polymer for shampoos that not only provides great softness to the hair but also, has the ability to reduce the formation of thermal cracks in
Fig. 4: SEM micrographs of two hair fibers, (a) from a hair tress with no treatment, and (b) from a hair tress treated with a rinse-off conditioner containing Tinocare SiA1
Fig. 5: Micrographs of hair fibers before and after subjected to 25 cycles of wetting and blow drying. One cycle: 25 sec immersion in a 1 to 5 shampoo dilution, 30 sec rinsing, and 30 sec blow drying at 80°C. Shampoos: 12% SLES-2, 3% CAPB, with 0.5% Luviquat Sensation (images on right) and no Luviquat Sensation (images on left).
1. Breakage of bonds in hair; this process can be quite damaging depending on how and what types of bonds are broken;
2. Re-arrangement of hair into its new geometrical configuration; this step usually is not damaging; and
3. Re-formation of broken bonds to “lock-in”the new geometrical configuration; in most cases this step is not damaging since its purpose is to reform broken bonds.
Fig. 6: Microscopic sequential images of a relaxed African hair fiber showing swelling behavior immediately after the fiber was put in contact with a neutralizing solution at a pH of 4.5.
This change in hair shape is permanent as it involves the breakage and reformation of covalent bonds. As it will be explained later, there is a certain level of hair damage during the breakage and reformation of bonds for permanent waving, however, it is not comparable to that occurring during alkaline straightening.
The process of permanent waving contrasts with that of water setting where the change in fiber shape is only transient and of short duration; i.e., the process does not involve the breakage of covalent bonds. In water setting, step 1 consists of breaking the weak hydrogen bonds in hair with water, just as the hair is wet. In step 2, once the weak hydrogen bonds are broken, the hair is set in a new configuration with rollers (to create curls) or with a hot iron to make it straight. In step 3, the new configuration is locked by reforming hydrogen bonds as water is extracted from hair with a blow dryer or with a hot iron. Most of the breakage of bonds in water setting involves only hydrogen bonds and, therefore, the process per se is not damaging at all.However, the frequent application of blow dryers and hot irons can cause thermal damage. The duration of water setting is transient and is rapidly reversed with moisture as water breaks again the formed hydrogen bonds.
In the case of hair straightening, step 1 consists in the breakage of disulfide bonds in hair by the hydroxide ions (OH- ions) present in the cream relaxer. The OH- ions are produced by the dissociation of sodium hydroxide, lithium hydroxide, or guanidine hydroxide. The breakage of disulfide bonds with OH- ions follows the β-eliminationreaction with the formation of crosslinks involving dehydroalanine and lanthionine. Some scientists believe that these crosslinks later stabilize the straightness of the relaxed hair.5 Others have proposed that fiber super-contraction with re-arrangement of the alpha-keratin into a less organized structure drives the changes in fiber shape from curly to straight. Both processes, however, require bond breakage.
Unfortunately, step 1 breaks disulfide bonds along with strong hydrogen bonds, salt linkages, and peptide bonds. Consequently, when hair is soaked in the alkaline cream it turns into a very soft and deformable fiber after 10-15 minutes. In step 2, which actually occurs in parallel with step 1, the soft curly hair is forced with the comb to be in a straight configuration while it is still embedded in the cream relaxer. Finally, in step 3 the new hair shape is finalized into its new straight configuration as the strong hydrogen bonds and salt linkages reform upon neutralization of the OH ions.
Alkaline relaxers induce so much damage to African hair not only because they break hydrogen bonds, salt linkages, disulfide bonds, and peptide bonds, but also because a large number of the broken bonds break irreversibly and, as a consequence, the hair fibers lose between 40-60% of their mechanical strength. For instance, experimental evaluations appear to indicate that during the process of alkaline relaxation about 40% of the disulfide bonds are irreversibly broken. After the neutralization process, only 6-10% of the broken bonds appear to recover.
Another source of damage in relaxed hair is excessive swelling during the process of neutralization (Fig. 6). This is caused by a strong osmotic pressure from the water outside the hair due to the high concentration of sodium and hydroxide ions inside the hair. This level of swelling, if not controlled during neutralization, stretches and ruptures cuticle cells.
The alkaline hair straightening process contrasts sharply with the permanent waving process. In the later, the breakage of bonds by ammonium thioglycolate is not indiscriminate, but selective only to disulfide bonds. Also, in permanent waving, approximately 90% of the broken bonds is reformed after the oxidation process. It is for this reason that in some countries such is in Brazil, one can find hair straighteners for African hair formulated with ammonium thioglycolate. The claim here is that these relaxers are less damaging to hair because of their selectivity to disulfide bonds. Although, some cosmetic scientists believe that hair straightened with ammonium thioglycolate relaxers later undergoes a process of reversion to its curly state.6
But most of the cream relaxers in the U.S. are alkaline, which severely damages hair. Efforts to solve this problem have led to the development of technology in three areas:
1. Design of new hair straightening systems that are less damaging than those involving OH ions. These systems include the ammonium thioglycolate relaxer and hair straightening with heat and formaldehyde.
2. Formulation of products that reduce hair damage during the alkaline straightening process. In this area we find the incorporation of cationic polymers to cream relaxers and the development of wax emulsifiers with controlled HLB to protect the hair cuticle sheath.
3. Creation of products or ingredients that prevent or reduce further damage to hair after the straightening process. This area includes most of the developed current maintenance products.
Fig. 7: Percentage reduction in dry combing work by a spray and a cream leave-on conditioner containing Tinovis CD, as described in reference 7.
When this cream is applied to hair as a leave on conditioner, the water-swollen beads adsorb onto the hair providing excellent lubricity to the hair surface. The polymer beads have the ability to keep high levels of moisture on the hair surface even after the hair dries. Furthermore, the cream formed by interlocking of the swollen polymer beads can disperse and emulsify a high level of hydrophobic actives making it an excellent carrier for silicone and other oils. Fig. 7 shows detangling workloads in relaxed tightly curly hair with two leave-on conditioners containing Tinovis CD.7
More info: Joel Basilan, regional development and technical service manager, hair and body care North America, BASF; Tel: 973-448-5303; Email: firstname.lastname@example.org;
1. R. Robbins, “Chemical and Physical Behavior of Human Hair,” 3th. Ed. Springer-Verlag, New York, 1994, pp. 211-206
2. Y. Kamath, and S.B. Hornby “Mechanical and Fractographic Behavior of Negroid Hair,”J. Soc. Cosm. Chem. 34, 25-43 (1984)
3. Y. Kamath, S.B. Hornby, H.D. Weigmann, “Effect of Chemical Humectant Treatments on the Mechanical and Fractographic Behavior of Negroid Hair,” J. Soc. Cosmet. Chem. 1985; 36(1); pp. 39-52
4. M. Gamez-Garcia, “The Cracking of Human Hair Cuticles by Cyclical Thermal Stresses,” J. Soc. Cosmet. Chem., 49, 141-153(1998)
5. L. J. Wolfram, “The Reactivity of Human Hair. A Review,” in Hair Research, Ed. by Orfanos, Montagna, Stuttgen and Springer-Verlag, Berlin Heidelgerg 1981
6. M. Wong, G. Wis-Surel, and J. Epps, “Mechanism of Hair Straightening,” J. Soc. Cosmet. Chem., 45, 345-352 (November/December 1994)
7. Spray Leave-in Conditioner: USPAD-D2070-43 “Spray Leave-In Conditioner;” Cream Leave-in conditioner: USPAD-D2070-3 “Smooth & Style Leave-In Conditioner.”