What is the main ingredient in products that completely straighten the hair?

• A. Sodium hydroxide
• B. Ammonium thioglycolate
• C. Guanidine hydroxide
• D. Potassium hydroxide

Answer: (A)

The main idea here is that permanent straightening uses a strong alkaline chemical to break the hair’s internal bonds so the strand can be reshaped straight, then a neutralizer rebuilds those bonds in the straight configuration. Sodium hydroxide is the classic ingredient used in traditional relaxers to achieve that complete straightening because its high pH effectively opens the cuticle and breaks the disulfide bonds inside the cortex, allowing the curl pattern to be reformed straight during processing. After shaping, the neutralizer stops the chemical reaction and re-bonds the hair in its new straight form. The other substances listed are used in different contexts: ammonium thioglycolate acts as a reducing agent primarily in perms to loosen curl rather than fully straighten, while guanidine hydroxide and potassium hydroxide appear in other relaxer formulations but are not the standard main ingredient for the typical complete straightening described in this scenario.