Thio relaxers should not be used on hair that has been treated with hydroxide relaxers.

• A. Hydroxide relaxers
• B. Keratin treatments
• C. Color safe shampoos
• D. Scalp peels

Answer: (A)

Thio relaxers and hydroxide relaxers both aim to loosen and straighten hair by breaking disulfide bonds, but they use incompatible chemistries at different pH levels. Hair treated with hydroxide relaxers has had its disulfide bonds permanently altered in a high-pH environment and requires careful neutralization and conditioning to rebalance the hair. Introducing a thioglycolate-based thio relaxer on this already-processed hair can push the bond-breaking too far, leading to overprocessing, uneven results, swelling, and severe breakage because the hair’s structure has already been compromised. Because of this, using a thio relaxer after hydroxide-relaxed hair is unsafe and should be avoided. Other options like keratin treatments, color-safe shampoos, or scalp peels do not involve applying a second bond-breaking chemical in the same way, so they don’t present this specific risk in sequence.