Science of hair waving

Introduction
Since ancient cultures curly hair represented femininity and beauty. Women with straight hair purchased expensive wigs or spent hours for hair ondulation with water and heat, which was temporary.
Ÿ Permanent hair waving is a two-step chemical treatment modifying hair protein to achieve and retain a curly shape.
Ÿ The chemical treatment involves a thioglycolate reduction reaction that plasticizes hair while being wound on a rod. The following oxidation step with hydrogen peroxide reforms the hair in a new curly shape.
Ÿ Curl retention depends on hair thickness, rod diameter, and hair quality.
Ÿ Undesirable hair damage can occur with the wrong choice of perm and neutralizer, too much heat, incorrect processing time, or improper perm solution amount.

Chemophysical principles of hair waving

Because of hair’s great elasticity and strong resilient forces, it quickly resumes its original straight shape. Therefore it has to be softened and subsequently rehardened chemically to maintain a conformation change. Especially with permanent waving, it is important to select a reversible reaction to allow repeated treatments without hair destruction. The sulfur bridges of the amino acid cystine, linking the proteins, are best suited.
The conditions for permanent waving to be well tolerated are:

Low temperature (20-50®C), convection or contact heat;
ŸShort process time (5-30 minutes); and
Mildness to the skin.

A permanent wave occurs with two solutions:
Solution 1: the perming lotion, which contains a reducing agent, a “thiol” compound, designed to split off about 20-40% of hair cystine bonds.
Solution 2 : a fixing lotion, which contains an oxidizing agent, usually hydrogen peroxide, designed to rebuild cystine bridges between proteins at new sites in the curled hair shape. It must be emphasized that permanent waving is a two-step procedure where the chemical reaction and physical effects run in parallel reduction of disulfide-bonds, softening of hair, lateral swelling and length contraction, stress development and protein flow, then re-oxidation of cystin bonds and deswelling, fixation of a new curly shape.