The Four Categories of Hair Color
Every hair color product on the salon shelf falls into one of four categories. The category controls how deep the color goes into the hair, how long it lasts, and whether it can lift natural pigment. State board exams test this constantly, so know the differences cold.
Temporary Color
Temporary color uses large pigment molecules that sit on top of the cuticle. They never enter the cortex. Because the molecules are too big to penetrate, they wash out in 1 to 2 shampoos. Think rinses, color mousses, and hair mascaras used between salon visits or for one-night events.
Semi-Permanent Color
Semi-permanent color uses medium-sized molecules that slip just under the cuticle layer and deposit in the outer edges of the cortex. It needs no developer and produces no lift. Expect 4 to 6 weeks of wear, fading gradually with each shampoo. Good for refreshing faded ends, adding fashion tones, or blending the first few grays.
Demi-Permanent Color (Deposit Only)
Demi-permanent is the workhorse for gloss services and gray blending. It mixes with a low volume developer, typically 5 or 10 volume, which gives just enough oxidation to open the cuticle slightly and lock the dye into the cortex. There is no lift, but the result is shinier than semi-permanent and lasts 4 to 6 weeks. Demis are popular because they fade softly without a hard regrowth line.
Permanent Color
Permanent color is mixed with a stronger developer, usually 10 to 40 volume, and contains an alkaline agent like ammonia. It lifts the natural pigment and deposits new color in the cortex at the same time. The result lasts until the hair grows out or is cut off. This is the only category that can truly lighten natural hair color.
What Is Happening Inside the Cuticle
Permanent hair color is an oxidation reaction. Two things happen at the same time inside the hair shaft: natural pigment gets broken down, and synthetic dye precursors join together to form new color molecules.
Melanin: The Natural Pigment
Hair gets its natural color from melanin, which lives in the cortex. There are two types:
- Eumelanin: the brown to black pigment. Dominant in dark hair.
- Pheomelanin: the red to yellow pigment. Dominant in red and blonde hair.
When hydrogen peroxide enters the cortex, it oxidizes melanin and breaks it into smaller, lighter fragments. This is what cosmetologists call lifting. The hair gets lighter as more pigment is destroyed.
Underlying Pigment Exposed by Lifting
Eumelanin breaks down faster than pheomelanin. That is why warm tones are revealed as hair lightens, even if the natural color looked cool. Dark hair shows red and orange first because the pheomelanin is still hanging on after most of the eumelanin is gone. Blonde hair shows yellow and pale yellow at the end of the lift.
| Starting Level | Underlying Pigment Revealed |
|---|---|
| Levels 1 to 3 (black to dark brown) | Red |
| Levels 4 to 5 (medium brown) | Red-orange |
| Level 6 (dark blonde) | Orange |
| Level 7 (medium blonde) | Orange-yellow |
| Level 8 (light blonde) | Yellow |
| Levels 9 to 10 (lightest blonde) | Pale yellow |
The Role of Ammonia
Ammonia (or a gentler alkaline equivalent like ethanolamine, sometimes labeled MEA) does three jobs in a permanent color formula:
- Raises the pH so the cuticle swells open. Hair has a normal pH around 4.5 to 5.5; permanent color sits closer to 9 to 10.
- Activates the peroxide so it can release oxygen and oxidize melanin.
- Carries dye precursors into the cortex while the cuticle is open.
Ammonia-free formulas use MEA or AMP instead. They smell less harsh and are gentler on the scalp, but they can be slightly less efficient at lifting. The job is the same: open the cuticle, activate peroxide, deliver dye.
Developer Volumes and What They Do
Developer is hydrogen peroxide diluted to a specific strength. The volume number on the bottle tells you how much oxygen the peroxide can release. Higher volume means more oxidation, which means more lift.
| Volume | Peroxide % | Action | Typical Use |
|---|---|---|---|
| 10 volume | 3% | Deposit only or 1 level of lift | Demi-permanent, toners, dark deposit-only formulas |
| 20 volume | 6% | 1 to 2 levels of lift | Standard gray coverage, tone-on-tone permanent color |
| 30 volume | 9% | 2 to 3 levels of lift | Going noticeably lighter on virgin hair |
| 40 volume | 12% | 3 to 4 levels of lift | High-lift blondes, used cautiously, never on the scalp |
Mixing Ratios
Most permanent and demi-permanent colors mix 1:1 with developer. One ounce of color to one ounce of developer is the default. Always check the manufacturer instructions because some lines vary.
High-lift blonde formulas are the main exception. They mix 1:2, meaning one part color to two parts developer. The extra developer gives the formula more lifting power, which is what high-lift shades are designed for.
Application Principles: Hot Scalp, Cool Ends
Body heat radiates off the scalp and speeds up chemical processing. Color applied at the root processes faster than color applied at the ends. This is called the hot scalp effect, and it changes how you sequence an application.
- Lifting on virgin hair: apply color to the mid-lengths and ends first, then come back to the scalp last. The scalp area only needs a fraction of the time the ends need.
- Color retouch on regrowth: apply only to the new growth at the scalp. Pull through to the ends in the last few minutes if needed for refresh, never the full processing time.
- Depositing on porous ends: apply ends first if they are very porous and need extra time to grab tone, but watch for over-deposit.
State Board Exam Topics
These are the questions students see most often on the chemistry of color section.
Which developer volume gives 2 levels of lift?
20 volume (6%) gives 1 to 2 levels of lift and is the standard for gray coverage and tone-on-tone work. 30 volume gives 2 to 3 levels.
What is the role of ammonia in permanent color?
Ammonia raises the pH so the cuticle swells open, activates the hydrogen peroxide, and lets dye precursors enter the cortex. All three answers are correct, but if the exam asks for the primary role it is opening the cuticle.
Which underlying pigment is exposed at level 7?
Orange-yellow. Level 6 is orange, level 7 is orange-yellow, level 8 is yellow.
Why does demi-permanent color not lift?
Demi-permanent is mixed with a low volume developer (5 or 10) and contains little or no ammonia. There is not enough oxidation or alkalinity to break down melanin. Demi only deposits new color; it cannot lighten what is already there.
Putting It All Together
Hair coloring oxidation comes down to a few clean rules. Permanent color uses ammonia and a developer of 10 volume or higher to open the cuticle, break down melanin, and deposit new dye in the cortex. Eumelanin breaks down first, which is why warm underlying pigment is exposed during every lift. The developer volume controls how many levels of lift you get. The category of color (temporary, semi, demi, permanent) controls how long the result lasts and whether lift is even possible. Memorize the developer chart, the underlying pigment chart, and the four categories. Most chemistry questions on the state board come straight from those three.