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In man, the hair fiber consists of the cuticle, cortex, and medulla. The cuticle surrounds the actual fiber and consists of Overlapping flat scale-like cells. The cuticle protects the hair fiber and is generally more resistant to penetration and attack by chemical agents. The cortex consists of spindle shaped cells which are oriented along the axis of the hair fiber. Microfibrils of the protein keratin are found in cortical cells. The medulla runs down the center of the hair fiber and usually consists of hollow cells.
Straightening or relaxing the hair fiber involves breaking the disulfide bonds found in the hair fiber proteins and reorienting them so that the hair fiber forms the desired "straight" configuration.
In the 1920's hair relaxers were generally soap based systems containing sodium hydroxide in conjunction with typical fatty acids such as stearic acid. These relaxers were often caused burning or stinging, thus a base of petrolatum was usually first applied to the hair.
In the 1950's it was discovered that if the Relaxer composition was presented in a water in oil emulsion form, the results were improved and the burning and stinging was considerably reduced. In such systems, the sodium hydroxide was dissolved in water. The water mixture was then dispersed or emulsified into an oil mixture to create a water in oil emulsion. As the formulators increased the concentration of the lye containing water phase, they added more oil to the relaxer formulation so that the formula was approximately 50 percent water phase and 50 percent oil phase. It was discovered that a 50/50 mixture of oil and water phases was optimum. A relaxer formulation with higher co
ncentrations of oil was more stable, but usually less effective in providing relaxing properties. On the other hand, a relaxer with increased amounts of water phase (and hence more effective as a relaxer) often was unstable, and caused burning and stinging upon application, particularly when the lye concentration became too high.
Then in the 1960's emulsion control was improved. It was discovered that relaxers were much improved when water phase was dispersed in the oil in a micelle configuration. The resulting relaxer formulation was still a water in oil emulsion containing about 50 percent water phase and about 50 percent oil phase, the difference being in the micellular configuration of the water/oil droplets. When the relaxer composition was applied to hair and massaged in, the micelle broke, released the water/lye mixture which then penetrated into the hair fiber cortex. The oil portion of the micelle rested on the cuticle and performed a conditioning effect. The result was a relaxer which was more stable, less painful to use, and much more commercially desireable.
Other systems evolved as formulators attempted to achieve the same relaxing effects but without the use of lye. A guanidine carbonate/calcium hydroxide system was developed and is still used today. In guanidine based systems, a water insoluble inorganic hydroxide such as calcium hydroxide is reacted with a water soluble guanidine salt such as guanidine carbonate. The guanidine hydroxide mixture is then applied to the hair and acts as an effective hair straightener, but quickly converts back to guanidine carbonate which has no hair straightening properties. Guanidine carbonate/calcium hydroxide systems are very popular and widely used today. They are somewhat milder than lye based systems, but are generally considered to be less effective in achieving straightening or relaxing effects.
Attempts to improve existing systems were complicated by the fact that the inventors were unable to determine any correlation between the following variables: the percentage of water in the formulation vs. the irritation Level, the ability of the relaxer formulation to penetrate hair vs. the irritation level, and the active level of sodium hydroxide vs. the irritation level within the limits of acceptibility.
In terms of straightening effectiveness, lye is still the ingredient of choice. Thus it is most desireable to use lye, yet to alleviate the other problems associated with its use.
Excerpt from Hair relaxer composition and associated methods
Photo courtesy of Georgia Based Salon - SalonBaptiste.com
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History of Relaxers