Which protein bond is most directly responsible for the permanent shape change that occurs in a thio relaxer or cold perm?
Explanation
Disulfide bonds (S-S cross-links between two cysteine amino acids in adjacent keratin chains) are the strongest of the three side bonds in hair. Permanent chemical reshaping is the controlled breaking and reforming of disulfide bonds: a reducing agent such as ammonium thioglycolate or ammonium sulfite donates hydrogen to break the bond, the hair is reshaped on a rod or pressed straight, and an oxidizing neutralizer rebuilds the disulfides in the new position. Salt and hydrogen bonds are too weak to hold permanent shape. Peptide bonds are the backbone of the protein and are NOT broken in routine chemical services. The relevant SDS under Cal/OSHA §5194 spells out the hazards of both reducers and neutralizers.
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