Final answer:
To perm coarse hair, the perm solution requires sufficient hydrogen ions, which are supplied by a reducing agent like ammonium thioglycolate, to break disulfide bonds before reshaping and setting the hair with an oxidizing agent.
Step-by-step explanation:
To perm coarse hair, the solution must have enough hydrogen ions to break the required number of disulfide bonds. The process of perming hair involves reducing the disulfide bonds in the hair's keratin structure, which are strong covalent bonds that give hair its shape and texture. An effective perm solution contains a reducing agent, typically ammonium thioglycolate, which supplies the necessary hydrogen ions to break disulfide bonds. After the hair is set on rollers, an oxidizing agent such as hydrogen peroxide is applied to re-form the disulfide bonds, fixing the hair in its new shape.