Ammonium thioglycolate (used in cold perms and thio relaxers) and sodium hydroxide (used in lye relaxers) differ in which fundamental way?
Explanation
Thioglycolate is a sulfur-containing reducing agent: it donates hydrogen to the disulfide bond, splitting it into two cysteine thiols, a reversible change that an oxidizing neutralizer can put back together. Sodium hydroxide is one of the strongest alkalis used on skin; at pH 12 to 14 it strips a sulfur atom out of the disulfide entirely, converting cystine to lanthionine, a permanent rearrangement that cannot be reversed and that is followed by a neutralizing (acidifying) shampoo rather than an oxidizer. The pH and mechanism differences explain why the two products MUST NOT be layered on the same hair without major breakage risk. SDS hazard information is required for both classes under Cal/OSHA §5194.
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