The Bleaching of Hair

But although all our knowledge begins with experience, it does not follow that it arises from experience. 

After World War I, other chlorine-based bleaches were developed. In 1921 the use of chlorine dioxide for bleaching fibers was reported followed by the development of the commercial process for large-scale production of sodium chlorite. In 1928 the first dry calcium hypochlorite containing 70 % available chlorine was produced in the United States. This material largely replaced bleaching powder as a commercial bleaching agent. 

The H2O2 solution is highly corrosive. Avoid skin contact and wear safety glasses and protective gloves. 

100-mL beaker, 250-mL beaker, glass rod, protective gloves, safety glasses. 

30 % H2O2 solution, 2 moi/L ammonia solution, acetone, dilute hydrochloric acid. 

---

Reactions involving the transfer of electrons are called oxidation-reduction reactions or redox reactions. Redox reactions are responsible for the rusting of iron, the bleaching of hair, and the production of electricity in batteries. Many redox reactions involve the reaction of a substance with oxygen. 

Oxidation and Reduction Redox reactions are common in nature, in industry, and in many everyday processes. Batteries use redox reactions to generate electrical current. Our bodies use redox reactions to obtain energy from glucose. In addition, the bleaching of hair, the rusting of iron, and the electroplating of metals all involve redox reactions. 

The bleaching of hair involves a redox reaction in which melanin— the main pigment in hair— is oxidized. 

Normal hair is slightly acidic. In fact, the pH of hair is between 4.5 and 5.5. Hair that becomes too alkaline dries out, tangles easily, becomes dull, and generally looks damaged. Chemical processes, such as permanent waves, hair coloring, and bleaching, as well as a person s natural body chemistry, can all raise the hair s pH. 

Cystine, which contains a disulfide bond, is reported to be the most numerous and reactive amino acid present in hair keratin. Disulfide bonds in cystine are reduced by mercaptans and phosphines, and oxidized by perborates, bromates, and bleach. These reactions result in structural rearrangements within keratin which may affect the physiochemical properties of hair, since disulfide bonds in cystine contribute to the stability of hair. For example, hydrogen peroxide bleaching of hair is an oxidative process which occurs readily in an alkaline medium. This results in the formation of perhydroxy anions which have been proposed to react with cystine to form cysteic acid residues. The process of bleaching results in the loss of approximately 15% of the cystine bonds originally present in keratin and may explain the increased permeability of bleached hair to chemicals. - ... 

The chlorinated derivative of dimethyl hydantion was the first solid bleach and was used in swimming pool chlorination [110]. Reacting dimethyl hydantion with formaldehyde produces mono- and dimethylol dimethylhydantion which are used as preservatives in cosmetics [111]. Monomethyloldimethyl-hydantion is converted into a resin used in the formulation of hair lacquers upon heating [112]. Dimethyl hydantion also is used in the synthesis of several a-amino acids, including phenylalanine found in aspartame [113]. 

Doses of chloroquine used for oral therapy of the acute malarial attack may cause GI upset, headache, visual disturbances, and urticaria. Pruritus also occurs, most commonly among dark-skinned persons. Prolonged medication with suppressive doses occasionally causes side effects such as headache, blurring of vision, diplopia, confusion, convulsions, lichenoid skin eruptions, bleaching of hair, widening of the QRS interval, and T-wave abnormalities. These complications usually disappear soon rffter the drug is withheld. Rare instances of hemolysis and blood dyscrasias have been reported. Chloroquine may cause discoloration of nail beds and mucous membranes. 

HEALTH SYMPTOMS inhalation (irritates eyes, nose and throat) contact (blistering of the skin, skin reddening, bleaching of hair, comeal ulceration). 

Concentrated solutions of hydrogen peroxide are very caustic and can cause bums of skin and mucous membranes. Exposure to its vapors can produce body irritation, lacrima-tion, sneezing, and bleaching of hair. A dose of 500 mg/kg by dermal route caused convulsions and deaths in rabbits. The oral LD50 value for 90% peroxide solution in mice is 2000 mg/kg. 

Since the bleaching of human hair is carried out in an aqueous alkaline oxidizing medium, hydrolysis of the cystine oxide intermediates (Figure... 

Cationic ingredients in general are highly substantive to hair because of hair s low isoelectric point, which is approximately pH 3.67 [24] in cosmetically unaltered hair, and even lower in bleached hair. Therefore, at any pH above the isoelectric, the surface of hair bears a net negative charge, and positively charged (cationic) ingredients are attracted to it. 

Chow [28] has provided evidence for penetration of the lower-molecular-weight PEI-6 into hair, and Woodard [42] has shown that sorption increases with concentration and with bleaching of hair similar to polymer JR. 

Bleaching increases the permeability of hair, but it also decreases the disulfide content, and the disulfide bonds are potential sites to form mercaptan groups, a part of the redox system. 

The chemistry of bleaching shows that a major side reaction in the beaching of hair involves the oxidation of cystine cross-links to cysteic acid residues. This disruption of cross-links has a major influence on the wet tensile properties of hair. 

---