For a long time, hair relaxers have been used to straighten hair thus making it easier to style. These hair relaxers straighten hair by destroying the protein composition of hair and the most effective active ingredients in these relaxers are Sodium Hydroxide and Guanidine hydroxide (Baran & Maibach, 2005). Hair is primarily composed of keratin which is a form of fibrous protein that is made up of long amino acid chains (polypeptides). In these chains, the amino acids are linked to one another through chemical bonds which are known as peptide bonds.
These polypeptide chains are linked to each other through salt, disulphide, and hydrogen bonds (Dale, 1997). These hydrogen bonds contribute greatly to hair strength and in fact their contribution forms a third of the total hair strength (Dale, 1997). These hydrogen bonds are so weak that they are easily broken by heat and water. Salt bonds just like hydrogen bonds are weak physical bonds and are broken easily by agents such as weak acid or alkaline solutions as well as pH changes. Unlike the other two, disulphide bonds are chemical in nature and are stronger and less.
However, they are susceptible to alkaline solutions. These disulphide bonds links the sulphur atoms found in cysteine to each other and they are the ones primarily responsible for hair’s strength. More hair strength is contributed by betaine. In an investigation done by Pulliainen et al. (2009) using high performance liquid chromatography, natural betaine was established to be a part of hair and it is believed to provide hair strength by helping to maintain the function of protein.
There are two types of keratin-soft and hard-and the one found in hair is the hard type. This type of keratin is insoluble in water and it is generally resistant to degradation by various agents for instance proteolytic enzymes (Sustaita, 2007). The keratin proteins in a hair fiber forms 65-95% of the fibers total weight (Keratin. Com, 2009). Hair is composed of various chemical elements which include carbon, hydrogen, sulphur, oxygen, and nitrogen.
Hair relaxers act on hair in two major ways-physical and chemical. The chemical action is due to breakage of disulphide bonds following the action of the alkalis found in hair relaxers. Since the disulphide bonds are the ones primarily responsible for providing hair strength as well as determining hair curls, breakage of these bonds leaves the hair soft (relaxed) and thus it can be manipulated (Dale, 1997). These alkalis also break the salt and hydrogen bonds further softening the hair.
The physical action comes about due to the breakage of the bonds leaving the hair free of natural curls thus it can be straightened by combing. In other words it changes hair physically from curly to straight thus giving it a new shape. Following application of hair relaxers, the structure of hair changes due to breakage of bonds but these bonds are reformed. Use of water and heat during relaxing breaks hydrogen bonds but these are reformed when the hair is dried and cooled.
The broken salt bonds are reformed by use of neutralizers (acids) which normalizes the hair pH. Disulphide bonds are also reformed following application of neutralizers but their position changes so that they hold hair in the new straight shape. The neutralizer also re-hardens hair. From the discussion above, it is clear that the hair relaxers targets the protein components of hair and it does this by destroying the bonds that link polypeptide chains together. After this breakage, neutralizers are applied and hair dried to reform these bonds.