Final answer:
The strength of a permanent wave is determined by the concentration of its reducing agent.
The reducing agent breaks the disulfide bonds in hair, allowing it to be reshaped, while an oxidizing agent reforms the bonds in the new shape.
Step-by-step explanation:
The strength of any permanent wave is based on the concentration of its reducing agent.
In the permanent wave process, a basic reducing substance, such as ammonium thioglycolate, is added to reduce and rupture some of the disulfide cross-links in the hair.
The reducing agent disrupts the disulfide bonds, allowing the hair to be reshaped.
Once the hair is reshaped, an oxidizing agent, usually hydrogen peroxide, is added to reform the disulfide bonds in their new positions.