The answer is hydroxide relaxers. Milady states it plainly: "Hydroxide relaxers are usually sold in base and no-base formulas."
Ammonium thioglycolate (thio) relaxers are a genuinely different relaxer chemistry — they work by a different mechanism than hydroxide relaxers and aren't the ones described with base/no-base formulations in the textbook. The two relaxer families get confused often because both are used for the same end goal (permanently straightening curl pattern), but the chemistry and the terminology around them are distinct.
Why this trips people up: the FadeJunkie question bank had this keyed to "ammonium thioglycolate" until a July 2026 textbook audit corrected it — the real answer, hydroxide, was sitting right there among the other answer choices.
Milady Standard Barbering, 6th ed., Ch. 17, p. 606: "Hydroxide relaxers are usually sold in base and no-base formulas."
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