Calcium thioglycolate, depilatory

Figure 3-1. Hair fiber after treatment with calcium thioglycolate (depilatory) (scanning electron micrograph).

Depilatories remove hair by chemical reaction. They contain a substance, usually sodium sulfide, calcium sulfide, or calcium thioglycolate, that disrupts the disulfide linkages in the hair and dissolves it. The formulations commonly contain a base such as calcium hydroxide to raise the pH and enhance the action of the depilatory. A detergent and a skin conditioner such as mineral oil are also generally added to depilatories. 

Depilatories epitomize the chemical destruction of hair and allow hair removal by scraping with a blunt instmment or by rubbing with terry cloth. Chemical depilatories are based on 5-6% calcium thioglycolate in a cream base (to avoid runoff) at a pH of about 12. The pH is maintained with calcium or strontium hydroxide. Hair destraction is rapid, requiring not more than about 10 min. Treatment with a depilatory is followed by careful rinsing with water and various conditioning products intended to restore the skin s pH to normal. This type of treatment does not destroy the dermal papilla, and the hair grows back. 

The sodium and anunonium salts of thioglycolic acid are used in cold waving of hair. These compounds work by breaking the disulfide bonds of hair proteins, which maintain the overall structure of hair (Section 27.6Q.The disulfide bonds are subsequently reformed by oxidation (Section 10.9G) in a second step. The calcium salt of thioglycolic acid is used as a depilatory that is, it is used to remove body hair. 

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