What type of chemical service changes the structure of hair temporarily?

The type of chemical service that changes the structure of hair temporarily is perming. When a perm is performed, it involves the use of chemical solutions that break and reform the disulfide bonds in the hair's keratin structure. This process allows the stylist to create curls or waves, which can be maintained for a period of time, typically lasting several weeks to a few months.

The key aspect of perming is that it alters the hair's structure without permanently changing its inherent properties, meaning that once the chemical effects wear off, the hair returns to its original texture. This temporary nature is critical for clients who may wish to try different styles without committing to a permanent change.

In contrast, relaxing services, while also chemically altering the hair, are intended to straighten hair and offer a more permanent transformation. Coloring does not change the structure of hair but alters its appearance by introducing pigment. Curling techniques applied with heat can create temporary curls but do not chemically alter the hair structure since they do not involve breaking any bonds. Thus, perming is the correct choice for a service that temporarily changes the structure of hair.