Why is a permanent wave not really permanent?

Question

Quizplus · Accepted Answer

A permanent wave involves breaking and reforming disulfide bonds in the hair to create curls or waves. However, these bonds can only be broken and reformed a finite number of times before becoming too damaged. As new, untreated hair grows in to replace the treated old hair, it is not affected by the permanent wave chemicals and remains straight. Therefore, a permanent wave is not truly permanent as it only affects the hair that is initially treated.

Why Is a Permanent Wave Not Really Permanent