There are three different types of chemical hair straighteners: thioglycollates, sodium hydroxide, and bisulfite straighteners. All of them act by breaking the chemical bonds in curly hair, permitting them to be rearranged.
Thioglycollates are the same chemicals found in permanent waving lotions. For hair straightening, however, they are used in stronger concentrations. Straighteners are sold in cream and lotion forms. When thioglycollate solutions are used for hair straightening, they are referred to as relaxing lotions. These are applied to the hair and allowed to work for about twenty minutes, during which time the hair should be combed continually so that it will hang straight. Then a neutralizer is added. Combing should continue until the hair is fixed into its new straight shape. Finally, the hair is shampooed, set on gaint rollers, and dried. Unfortunately, thioglycollate straightners frequently do not give the desired degree of straightening.
Given their potential hazards, sodium hydroxide straighteners are limited ti salon usage. Sodium hydroxide, a very potent alkali, works on the hair rapidly-usually within five to ten minutes-to break the natural protein bonds. The hair then quickly relaxes with combing. A thorough rinsing of the hair neutralizes the chemical. However, the potential for several scalp and skin irritation and burns exists, so precautions, such as protecting the skin near the scalp with a thick cream, should be taken. Extreme care should also be taken to protect the eyes, since blindness could result.
Bisulfite straighteners, sometimes referred to as “curl-relaxers” are the most widely used home straightening agents. The bisulfite is applied to a damp scalp and then covered by a plastic cap for about fifteen minutes. This breaks chemical bonds in hair. Next the hair is rinsed and covered with an alkaline stabilizer. Bisulfite straighteners are generally mild on your hair and scalp, and effective.