7.1 Permanent waving & chemical relaxing

The chemistry of chemical texture

Chemical texture services — permanent waving and chemical relaxing — permanently change the shape of the hair by breaking and reforming the strongest bonds inside the cortex. This is the most safety-critical chemistry on the NIC written exam, so learn the reactions, not just the product names.

The three side bonds

Hair keratin is held together by cross-links, called side bonds, between its polypeptide chains. Three types matter:

• Hydrogen bonds are physical (temporary) bonds broken by water and heat; they make wet sets and thermal styling possible and account for about one-third of the hair's strength.
• Salt bonds are physical bonds broken by strong changes in pH; they supply another third of the strength.
• Disulfide bonds are chemical bonds that join the sulfur atoms of two cysteine amino acids to form cystine. They are the strongest side bonds and can only be broken by a chemical service or extreme heat.

Every perm and relaxer works the same way in principle: break the disulfide bonds, move the hair into a new shape, then rebuild the bonds so the new shape holds. Before any service, evaluate porosity, elasticity, texture, and density — porous hair absorbs product and processes faster, so it may need a milder formula and closer timing.

Permanent waving

A perm has a physical phase — wrapping the hair on rods — and a chemical phase — the waving lotion and the neutralizer.

The waving (reducing) lotion breaks disulfide bonds by adding hydrogen, a reduction reaction. The usual reducing agent is ammonium thioglycolate (ATG), or "thio."

• Cold (alkaline) waves use ATG at pH 8.2–9.6 and process at room temperature without added heat.
• True acid waves use glyceryl monothioglycolate (GMTG) at pH 4.5–7.0 and are endothermic — activated by an outside heat source such as a hood dryer.
• Exothermic waves produce their own heat through an oxidation reaction mixed in just before application.

The rod controls the curl: the smaller the rod diameter, the tighter and smaller the curl; a larger rod makes a larger, looser wave. In a croquignole wrap the hair is wound from the ends toward the scalp; a spiral wrap winds the strand down the length of the rod to give a uniform curl on long hair. End papers and even tension keep the ends smooth.

Neutralizing, also called fixation, rebuilds the disulfide bonds. The neutralizer is an oxidizer — commonly hydrogen peroxide or sodium bromate — that removes the hydrogen the waving lotion added and locks the bonds into the shape of the rod. Always rinse the waving lotion thoroughly and blot each rod before applying neutralizer. During processing, take test curls to check the strength of the S-shaped wave before rinsing.

Chemical relaxers

Relaxers straighten by breaking disulfide bonds so the hair can be smoothed flat. There are two families:

• Hydroxide relaxers — sodium hydroxide ("lye"), plus guanidine hydroxide and lithium hydroxide ("no-lye") — straighten by lanthionization: they remove a sulfur atom and permanently convert the disulfide bond to a lanthionine bond. Because this change is irreversible, hydroxide relaxers are never rebonded with an oxidizer. Instead an acid-balanced neutralizing (normalizing) shampoo lowers the pH and stops the action.
• Thio relaxers use ammonium thioglycolate at about pH 10 — stronger than a thio perm. They reduce the bonds, the hair is smoothed straight, and an oxidizing neutralizer rebonds it, exactly like a perm.

Because these two chemistries are incompatible, never apply a thio relaxer over hydroxide-treated hair, or the reverse — the result is severe breakage. On pH and strength, sodium hydroxide relaxers are the strongest at roughly pH 11.5–14; no-lye guanidine formulas run slightly lower but tend to dry the hair because of calcium residue; thio relaxers sit near pH 10, and cold-wave lotions are the mildest at pH 8.2–9.6. As a rule, the higher the pH, the faster and more aggressively the product works, and the more carefully it must be timed.

Base vs. no-base: a base relaxer requires the stylist to apply a protective petroleum base cream to the scalp and hairline before the product; a no-base (self-basing) relaxer contains a protective ingredient that melts at body temperature, though the hairline, ears, and any abrasions are still protected by hand.

Virgin application vs. retouch: on a first-time (virgin) relaxer, apply product to the middle of the strand first — starting about a quarter inch off the scalp — because the scalp's body heat speeds processing near the base and the ends are the most porous and fragile. Save the scalp area and the most resistant sections for last, then smooth. On a retouch, apply only to the new growth and never overlap onto hair that was relaxed at the previous service, since double-processed hair breaks.

Strand tests, timing, and safety

During relaxing, take a periodic strand test — smooth the strand and watch how quickly it reverts — to judge the degree of relaxation without over-processing. Time every service and never exceed the manufacturer's window, because over-processing destroys the hair's integrity. Before any service, analyze the scalp and never relax over abrasions or an irritated scalp. Avoid overlapping product onto previously treated hair — the leading cause of relaxer breakage — always wear gloves, keep product out of the eyes, and rinse completely with warm water when processing is complete.