What effect does permanent waving have on hair?

Permanent waving alters the hair's shape by transforming straight strands into curls or waves through a chemical process. This procedure involves reshaping the disulfide bonds within the hair, which allows the hair to retain new styles that differ from its original texture. By applying a waving solution and then neutralizing the hair after it has been wrapped in curlers, the hair's internal structure is changed, leading to the formation of permanent curls or waves.

The other options do not accurately describe the effect of permanent waving. For instance, while some oils may be depleted during the chemical process, the treatment does not completely remove all natural oils from the hair. Similarly, permanent waving does not inherently strengthen hair; it can sometimes lead to damage if not performed correctly or if aftercare is neglected. Lastly, permanent waving does not increase hair length; it changes the shape of the existing hair rather than affecting its overall length.