The Chemistry Behind Perming

Each strand of hair on your head is made up of proteins, which contains a cortex at the centre. The cortex are also made up of proteins which are peptides linked together by peptide bonds in straight bundles. Peptides are two or more amino acids linked together. “An amino acid is a compound with a carboxyl group and amino group attached to a carbon atom” (DiGiuseppe 1). 

The medulla is what surrounds the cortex, and it contains hair pigment which provides your hair with color. Salt bonds, hydrogen bonds and disulfide bonds are three types of bonds found in the hair. The disulfide bonds in hair are what get changed while perming your hair. 

   Surrounding the cortex and the medulla is a sheath called the cuticle. The cuticle is made up of keratin and is what protects the hair.  The size of the cuticle can vary; some people may have hair with a tightly closed cuticle, and some may not. The arrangement of the cuticle determines the physical properties of the hair itself.
In hair, keratin molecules are packaged in bundles, which are held together by disulfide bonds
(-S-S-).

Disulphide bonds are made by the amino acid cysteine. The cysteine of each keratin molecule form disulfide bonds with each other, connecting the keratin molecules together. If there are more disulphide bonds in a strand of hair, the hair is straighter.

Ammonium Thioglycolate (HSCH₂CO₂NH4) is a compound found in perm which breaks the disulphide bonds, due to the fact that it contains a thiol group (-SH). An equation to express the breakage of disulfide bonds with Ammonium thioglycolate:

Keratin-S-S-keratin + 2HS-CH₂CO₂NH₄ --> -HO₂CH₂CS-SCH₂CO₂H + 2NH₃ + 2HS-keratin

When the hair is wrapped on a perm rod or rollers, ammonium thioglycolate (used in perm lotion) breaks the disulfide bonds  which held the previous wave pattern. When the disulphide bond is broken, the keratin molecules are separated making the hair weaker. Thus, being able to be styled easier and changing the hair texture. Afterwards, the lotion is rinsed and the rods are removed and a neutralizer is added, which reforms the new curl pattern.