What chemical process is used to change the structure of hair?

Chemical straightening or relaxing is the process that specifically alters the structural composition of hair. This method typically involves the use of strong chemicals that break and reform the bonds in the hair shaft, thereby reshaping the hair. The most common chemicals found in these products are sodium hydroxide or ammonium thioglycolate, both of which effectively change the hair's natural curl pattern to a straighter form.

In contrast, heat styling does not change the hair structure but temporarily alters its shape using thermal tools like curling irons or straighteners. Hair coloring involves the application of dyes or bleaches to alter the hair's color, but it does not modify the hair’s structural bonds. Deep conditioning treatments enhance moisture and repair damage on the hair surface but also do not affect its internal structure. Thus, the only option that describes a process capable of changing the underlying structure of hair is chemical straightening or relaxing.