What procedure involves reducing swelling of the hair and hardening its bonds during a perm?

The procedure that involves reducing swelling of the hair and hardening its bonds during a perm is applying the perm solution. This step is crucial because the perm solution contains chemicals that break down the disulfide bonds in the hair. When the solution is applied, the hair's cuticle swells, allowing the chemical to penetrate and alter the hair structure. Once the desired amount of time has passed, the hair is then set in the desired shape, and neutralizer is applied afterward to harden those newly formed bonds, effectively locking the curl pattern into place. The application process is the foundation for creating lasting curls or waves, making it a pivotal part of the perming procedure.