Why Chemistry Is So Important on the State Board Exam
Chemistry questions appear on every cosmetology state board exam, and they are among the most commonly missed questions. Many cosmetology students focus on hands-on skills and neglect the theoretical chemistry that underlies those skills. This is a mistake — understanding the chemistry not only helps you pass the exam, it helps you understand why chemical services work and how to troubleshoot problems in the salon.
The pH Scale: The Foundation of Cosmetology Chemistry
The pH scale measures the acidity or alkalinity of a substance on a scale from 0 to 14. A pH of 7.0 is neutral (pure water). Substances with a pH below 7.0 are acidic; substances with a pH above 7.0 are alkaline (also called basic).
For cosmetology, the key pH values to know are:
- Healthy hair: pH 4.5-5.5 (slightly acidic)
- Healthy skin: pH 4.5-5.5 (slightly acidic)
- Permanent wave solution (ammonium thioglycolate): pH 9.0-9.6 (alkaline)
- Neutralizer for permanent waves: pH 3.5-7.0 (acidic to neutral)
- Chemical relaxer (sodium hydroxide): pH 12-14 (strongly alkaline)
- Hair color (oxidative): pH 9.0-10.5 (alkaline)
- Acid-balanced shampoo: pH 4.5-5.5 (slightly acidic)
- Clarifying shampoo: pH 6.5-7.5 (near neutral to slightly alkaline)
Permanent Waves: How They Work
Permanent waves use a two-step chemical process to change the shape of the hair:
Step 1: Waving lotion (reduction). The waving lotion contains ammonium thioglycolate (ATG), which breaks the disulfide bonds in the cortex of the hair. These bonds give hair its strength and natural shape. When the bonds are broken, the hair becomes soft and pliable and takes the shape of the rods it is wrapped around.
Step 2: Neutralizer (oxidation). The neutralizer contains hydrogen peroxide or sodium bromate, which reforms the disulfide bonds in the new shape determined by the rods. This process is called oxidation. Once the bonds are reformed, the new curl pattern is permanent.
The key chemistry concept: waving lotion = reduction (breaks bonds); neutralizer = oxidation (reforms bonds).
Chemical Relaxers: How They Work
Chemical relaxers permanently straighten curly or wavy hair by breaking the disulfide bonds in the cortex and reforming them in a straighter configuration.
Sodium hydroxide relaxers (lye relaxers) have a pH of 12-14 and are the strongest type. They work quickly and provide the straightest results but can cause significant damage if left on too long.
No-lye relaxers use calcium hydroxide and guanidine carbonate (or lithium hydroxide or potassium hydroxide) instead of sodium hydroxide. They have a slightly lower pH (9-11) and are gentler on the scalp, but they can leave calcium deposits in the hair that cause dryness.
Ammonium thioglycolate relaxers (thio relaxers) use the same chemical as permanent wave solution but at a higher concentration and without rods. They are the mildest type and are best for slightly wavy hair.
Hair Color Chemistry
Hair color is categorized into four types based on how long the color lasts and how it works:
Temporary color — coats the outside of the cuticle without penetrating. Lasts until the next shampoo. No developer required.
Semi-permanent color — partially penetrates the cuticle. Lasts 4-6 shampoos. No developer required.
Demi-permanent color — penetrates the cortex slightly. Lasts 12-24 shampoos. Uses a low-volume developer (5-10 volume hydrogen peroxide).
Permanent color — fully penetrates the cortex and permanently changes the hair color. Uses a developer (20-40 volume hydrogen peroxide). The developer provides the oxygen needed for the oxidation reaction that develops the color.
The key chemistry concept for permanent color: the alkaline color formula opens the cuticle, the developer oxidizes the color molecules inside the cortex, and the color molecules become too large to escape through the cuticle.
Hydrogen Peroxide Developer Volumes
Developer is measured in volumes, which indicates the amount of oxygen it releases:
- 10 volume (3%) — minimal lift, used for deposit-only color and toning
- 20 volume (6%) — 1-2 levels of lift, the most common developer for permanent color
- 30 volume (9%) — 2-3 levels of lift, used for significant lightening
- 40 volume (12%) — maximum lift, used for high-lift color
Higher volume developers provide more lift but also cause more damage to the hair. Using the correct developer volume for the desired result is both a chemistry concept and a safety consideration.