A basic solution of ammonium thioglycolate, a.k.a. perm salt, is applied to the hair. The excess ammonia present in the solution helps the hair swell so that the reagents can work their way through each strand of hair, and also deprotonates the thioglycolate molecule, enabling it to break open disulfide bridges. At this point, the hair is wrapped around a curling rod and sprinkled with an oxidizing solution containing hydrogen peroxide. The disulfide bonds are reformed and the hair comes off the rod with a curl.
Anyone who has worked in a chemistry lab knows that yields are rarely ever one hundred percent. The same goes for the reactions on your hair. Not all the disulfide bonds that are broken by the thioglycolate will reform in the presence of hydrogen peroxide.
This is my mom!
This decrease in the total number of disulfide bonds is why people who perm their hair often likely notice a decrease in the strength and rigidity of their hair— also known as damage. But it varies from person to person.
It’s funny because to this day, I still remember the sulfurous rotten-egg smell that would fill the bathroom whenever my mom permed her hair. I remember watching her use the solutions in sequence, wondering how it all worked.