Hair is composed of a type of protein called keratin that is formed within the hair follicle, a cavity in the skin surrounded by cells that provide the amino acids and other components needed for protein formation. Genetics dictates the specific fashion in which the follicle assembles these components into the three-dimensional structure proteins, and it is this structure that then determines if an individual鈥檚 hair will be curly or straight.
Proteins are chains of amino acids that can be coiled in various ways. Keratin takes the shape of a helix, with the shape being maintained by 鈥渉ydrogen bonds,鈥� a weak attraction between oxygen and hydrogen atoms in adjacent coils. To complicate matters, these coiled keratin helices are twisted into different shapes as a result of cysteine, one of the amino acids in keratin, binding to another cysteine fragment in a different part of the chain. Specifically, it is the sulphur atoms in cysteine that form sulphur-sulphur bridges. To change the shape of the hair, the various bonds responsible for the keratin structure have to be first disrupted. With these bonds broken, the chain can move around more freely in response to the stresses created by combing or the placement of curlers. If at this point the bonds responsible for maintaining the structure of keratin can be reformed, the keratin, and hence the hair fibers will have been permanently reshaped. New hair growth will be unaffected.
Hydrogen bonds are easily broken just by exposure to water. That is why wet hair can be readily shaped. Heat, such as with a hair iron, will cause the water to evaporate and allow the hydrogen bonds to reform, keeping the hair in its new shape until moisture intervenes. To have the shape be altered permanently, the sulphur-sulphur bonds have to be broken and then reformed after the keratin molecules have been reconfigured. The chemical that has traditionally been used to break these bonds is the rather unpleasant smelling thioglycolic acid. Linking of the sulphur atoms in their new position is brought about with hydrogen peroxide. In the hands of experts, results are generally good but control of bond breakage and bond formation is not easy to control and timing is critical. Too long exposure to the chemicals can damage hair and too short can yield unsatisfactory results.
Another method of straightening or at least defrizzing hair relies on a different kind of chemistry. Often referred to as 鈥淏razilian blowout鈥� it involves adding a solution of keratin to the hair along with a binding agent to links it to hair鈥檚 own keratin. Heat is applied as a flat iron is used to straighten I while the applied keratin diffuses into the hair and crosslinks to maintain the new shape. The problem is that the binding agent is usually formaldehyde, which is a toxic compound and a known carcinogen. Indeed, a recent study has shown an increase in breast cancer, particularly in black women since Brazilian blowout was introduced. No such increase was seen when thioglycolic acid-based straighteners were used.
Of course there is another option. Enjoy your hair, curly or straight.
