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.
Permanent hair waving is a
two-step chemical treatment modifying hair protein to achieve and retain a
curly shape.
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.
Curl retention depends on
hair thickness, rod diameter, and hair quality.
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;
Short 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.
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