Permanent Wave Chemistry for the Cosmetology Exam

What a Perm Actually Does to Hair

A permanent wave changes the shape of hair by breaking and reforming the strongest bonds inside the cortex. The cortex is the middle layer of the hair strand, and it is where all the chemistry happens. Anything you put on hair during a perm has to pass through the cuticle scales to reach the cortex, which is why porosity matters so much for timing.

The bonds that perms target are called disulfide bonds. These are sulfur to sulfur links between two cystine amino acids. They are the strongest of the side bonds in hair, and they are what give hair its strength and its natural shape. If you change the disulfide bonds, you change the shape of the hair. If you do it correctly, you keep the strength too. If you do it wrong, you get damage, breakage, or a curl that falls out in two weeks.

The Three Side Bonds in Hair

Cosmetology students should be able to name and describe all three side bonds. They show up on every state exam.

• Hydrogen bonds: weak physical bonds, easily broken by water and heat, restored when hair dries. This is what wet sets and blow-dry styling rely on.
• Salt bonds: weak physical bonds broken by changes in pH (strong acids or strong alkalis). They reform when pH returns to normal.
• Disulfide bonds: strong chemical bonds broken only by chemical reduction (perms, relaxers, thio depilatories). They are reformed by oxidation.

A perm is the only one of the three common chemical services that breaks and reforms disulfide bonds in a controlled way to create a new permanent shape. Hydrogen and salt bonds break and reform every time you wash and style hair, so they cannot hold a new shape long term.

The Two Step Chemistry of a Perm

Every perm, no matter what brand or type, follows the same two step chemistry. Knowing these two steps cold is one of the easiest ways to pick up exam points.

Step 1: Reduction (the Waving Lotion)

The waving lotion is a reducing agent. It adds hydrogen to the disulfide bonds, which breaks them apart. With the disulfide bonds broken, the hair becomes soft and pliable and takes on the shape of whatever it is wrapped around. Common reducing agents on the exam:

• Ammonium thioglycolate (ATG): the classic alkaline (cold) wave reducer.
• Glycerol monothioglycolate (GMTG): the typical acid wave reducer, gentler than ATG.
• Sulfites and bisulfites: the mildest reducers, used in body waves and very gentle perms.

The reducing agent is also called a thio when it contains a thioglycolate. Thio is just shorthand for sulfur containing reducing agent.

Step 2: Oxidation (the Neutralizer)

Once the hair is wrapped on the rods and processed, you rinse out the waving lotion and apply the neutralizer. The neutralizer is almost always hydrogen peroxide. It removes the hydrogen the reducer added and rebuilds the disulfide bonds in the new curled position. After neutralizing, the curl is set permanently.

If you skip the neutralizer or rinse it out too early, the disulfide bonds never reform and the curl drops out. If you over-process with the waving lotion, you break too many bonds and the hair turns to mush. Both are reasons to take the strand test seriously.

Key Exam Point: The waving lotion breaks disulfide bonds by reduction. The neutralizer reforms disulfide bonds by oxidation. Two opposite chemical reactions, both targeting the same sulfur to sulfur link.

Types of Permanent Waves

The state exam expects students to match perm types with their reducing agent, pH range, and processing method. The table below covers the main categories.

Alkaline (Cold) Wave

The alkaline wave uses ammonium thioglycolate at a pH of 8.0 to 9.5. The high pH swells the cuticle so the lotion can reach the cortex quickly. It processes at room temperature without any added heat. The result is a strong, firm curl. Alkaline waves are good for resistant hair and for clients who want a tight, long lasting curl. They are harsher on the hair shaft because of the high pH.

Acid and True Acid Waves

Acid waves use glycerol monothioglycolate at a lower pH, between 4.5 and 7.0. A true acid wave sits right around 6.9. Because the pH is closer to that of the hair itself (around 4.5 to 5.5), acid waves are gentler. The trade off is that they need heat to drive the chemical reaction, which is why a true acid wave is processed under a hood dryer. Acid waves are the right choice for fine, fragile, or color treated hair where an alkaline wave would be too aggressive.

Endothermic vs. Exothermic Acid Waves

Both are acid waves, but they differ in where the heat comes from.

• Endothermic: needs heat from an outside source (a hood dryer or a heat cap). The word endo points outside in.
• Exothermic: uses an activator that creates its own heat through a chemical reaction. No dryer needed.

Sulfite Wave

Sulfite waves use sulfite or bisulfite reducers. They are the mildest of the perm chemistries and produce a soft, loose result. Often used as body waves on already fragile hair.

Common Mistake: Students mix up which wave needs heat. The rule: alkaline waves do not need heat because the high pH is already doing the work. Acid waves need heat because the lower pH is gentler and the reaction needs the extra energy to move forward at a usable speed.

The Strand Test

A strand test is a small test on a few rods or a single section of hair before processing the full head. It tells you three things:

1. Timing: how long it takes for the curl to develop on this client's hair.
2. Shape: whether the rod size and wrapping technique give the curl pattern the client wants.
3. Damage tolerance: whether the hair can handle the formula without breaking, stretching too far, or feeling mushy.

To check a strand test, unwrap a rod gently and let the hair fall into a loop. If the loop matches the diameter of the rod, it is processed. If the loop is loose, it needs more time. If the hair feels gummy or breaks, the formula is too strong for that hair.

Hair Texture and Porosity

The same perm formula can give very different results on different hair. Two big variables to watch:

• Porosity: how easily hair absorbs liquid. Porous hair (damaged, color treated, sun exposed) processes faster and may need a milder formula or a shorter timing. Resistant hair (smooth cuticle, virgin hair) needs a stronger lotion or a longer time.
• Texture: the diameter of each individual strand. Coarse hair has the largest diameter and resists chemical penetration. Fine hair processes fastest and is most fragile.
• Density: the number of hairs per square inch. Density affects sectioning and rod placement, not the chemistry itself.

The general rule: if the hair is porous or fine, lean toward the gentler formula and check the strand test early and often. If the hair is resistant or coarse, lean toward the stronger formula and expect a longer processing time.

Clinical Tip: Always do a porosity check before formulating. Slide your fingers from the ends toward the scalp on a dry strand. If it feels rough, the cuticle is open and the hair is porous. If it feels smooth, the hair is resistant. This 10 second check saves perms.

Quick Recap of High Yield Exam Facts

• Perms break disulfide bonds by reduction and reform them by oxidation.
• The waving lotion is a thio reducing agent (ATG, GMTG, or sulfite).
• The neutralizer is hydrogen peroxide, which oxidizes the bonds back together in the new shape.
• Alkaline waves: pH 8.0 to 9.5, ATG, room temperature, strong curl.
• Acid waves: pH 4.5 to 7.0, GMTG, heat assisted, gentler curl.
• True acid waves need a hood dryer; exothermic acid waves generate their own heat.
• Strand tests confirm timing, curl shape, and damage tolerance before committing to the full head.
• Porous hair processes faster and needs a milder approach. Resistant hair needs more strength or more time.