8.2 Classifications of Haircolor: Temporary, Semi, Demi & Permanent

Overview of Haircolor Chemistry

Professional haircoloring products are divided into four primary categories based on their chemical composition, molecular size, depth of hair shaft penetration, and developer requirements:

1. Temporary Haircolor (Non-oxidative)
2. Semi-Permanent Haircolor (Non-oxidative)
3. Demi-Permanent Haircolor (Oxidative deposit-only)
4. Permanent Haircolor (Oxidative lift and deposit)

Additionally, cosmetologists must understand non-professional formulations—specifically natural vegetable dyes (Henna) and metallic/progressive dyes—due to their extreme chemical volatility when exposed to salon oxidizers.

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1. Temporary Haircolor

Temporary haircolor is a non-oxidative color formulation that produces physical color changes without altering the internal chemical structure of the hair.

• Molecular Structure: Consists of extremely large, direct dye molecules.
• Penetration Depth: Pigment molecules are too large to pass through the cuticle scales; they adhere purely to the surface of the cuticle layer.
• Developer Requirement: None. No chemical reaction or oxidation occurs.
• pH Range: Mildly acidic to neutral (pH 7.0 – 8.0).
• Longevity: Removed completely in one shampoo.
• Clinical Purpose & Forms: Available in color rinses, mousses, gels, sprays, and color-depositing shampoos. Ideal for neutralizing yellow cast in gray hair, neutralizing discoloration, or special-event fashion coloring.

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2. Semi-Permanent Haircolor

Semi-permanent haircolor is a non-oxidative, direct-dye system that introduces smaller pigment molecules to achieve moderate color deposit.

• Molecular Structure: Composed of small-to-medium direct dye molecules.
• Penetration Depth: Pigment molecules partially penetrate through the cuticle into the outer layers of the cortex, while larger molecules remain on the cuticle surface.
• Developer Requirement: None. Applied directly from the bottle without mixing with hydrogen peroxide.
• pH Range: Mildly alkaline (pH 7.5 – 8.5).
• Longevity: Typically lasts 4 to 8 shampoos, fading progressively with each wash.
• Line of Demarcation: Does not produce a noticeable line of demarcation as new growth emerges because color fades evenly across the strand.
• Gray Coverage: Blends low percentages of gray (up to 20-30%) with a translucent tone; cannot lift or lighten natural hair.
• Safety Mandate: If formulated with aniline derivative precursors, a patch test is required 24–48 hours prior to application.

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3. Demi-Permanent Haircolor (Deposit-Only Color)

Demi-permanent haircolor is an oxidative haircolor system formulated to deposit artificial color without lifting or lightening the natural melanin in the hair cortex.

• Molecular Structure: Contains small oxidative color precursors that combine within the cortex.
• Penetration Depth: Penetrates fully into the cortex layer.
• Developer Requirement: Mixed with a low-volume hydrogen peroxide developer (typically 5-volume to 10-volume / 1.5% to 3%).
• Alkalizing Agent: Generally formulated with monoethanolamine (MEA) or aminomethylpropanol (AMP) instead of ammonia, minimizing cuticle swelling and avoiding natural melanin lightening.
• Longevity: Retains vibrancy for 4 to 6 weeks (fading over 20 to 28 shampoos).
• Clinical Indications:
  • Blending up to 50% gray hair without creating a solid line of demarcation.
  • Toning pre-lightened or double-processed hair.
  • Refreshing faded mid-lengths and ends during a permanent color retouch service (color glazing).
  • Corrective color filling (restoring missing undertones prior to going darker).

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4. Permanent Haircolor

Permanent haircolor is the gold standard for full gray coverage and simultaneous lifting and depositing in a single chemical process.

• Molecular Structure & Chemistry: Formulated with tiny uncolored oxidative dye precursors known as aniline derivatives (primarily paraphenylenediamine [PPD], toluene-2,5-diamine, and resorcinol).
• Chemical Mechanism:
  1. Cuticle Swelling: An alkaline agent (usually ammonium hydroxide / ammonia, pH 9.0–10.5) softens and swells the cuticle scales, allowing dye precursors to enter the cortex.
  2. Diffusion: The microscopic uncolored precursors diffuse deep into the cortex.
  3. Oxidation & Polymerization: When hydrogen peroxide developer meets the precursors, it releases oxygen. This oxidizes natural melanin (lifting natural level) while simultaneously coupling the precursors into large, colored polymer molecules.
  4. Trapping: Because the newly formed dye molecules are significantly larger than the precursors, they become permanently trapped within the keratin matrix of the cortex.
• Developer Requirement: Mixed with 10, 20, 30, or 40-volume developers.
• Gray Coverage: Provides 100% opaque gray coverage.
• Line of Demarcation: Produces a visible line of demarcation as new growth emerges, necessitating retouch applications every 4 to 6 weeks.

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Comparative Matrix of Haircolor Classifications

┌─────────────────┬─────────────────┬────────────────────┬───────────┬──────────────┬──────────────┬──────────────┐
│ Classification  │ Molecular Size  │ Penetration Depth  │ Developer │ Longevity    │ Gray Effect  │ Lift Ability │
├─────────────────┼─────────────────┼────────────────────┼───────────┼──────────────┼──────────────┼──────────────┤
│ Temporary       │ Very Large      │ Cuticle surface    │ None      │ 1 shampoo    │ Surface coat │ None (0)     │
│ Semi-Permanent  │ Small / Medium  │ Cuticle & outer    │ None      │ 4-8 shampoos │ Blends 20%   │ None (0)     │
│ Demi-Permanent  │ Small oxidative │ Deep cortex        │ Low (5-10)│ 4-6 weeks    │ Blends 50%   │ None (0)     │
│ Permanent       │ Microscopic     │ Deep cortex        │ 10-40 Vol │ Permanent    │ 100% opaque  │ 1-4 Levels   │
└─────────────────┴─────────────────┴────────────────────┴───────────┴──────────────┴──────────────┴──────────────┘

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Natural Vegetable & Metallic Dyes

Cosmetologists regularly encounter non-professional colorings that pose extreme chemical hazards during salon services.

Vegetable Haircolors (Natural Dyes)

• Henna: Derived from the leaves and powdered stems of the shrub Lawsonia inermis. Produces red-orange tones.
• Action: Henna binds tenaciously to keratin proteins on the outer cuticle and cortex, creating a thick, impenetrable coating.
• Incompatibility: Coats the hair shaft and prevents penetration of salon chemicals. Perming, relaxing, or lightening henna-treated hair causes extreme dryness, uneven processing, and severe breakage.

Metallic & Progressive Haircolors

• Composition: Contain metallic salts (lead acetate, silver nitrate, copper sulfate) that react with sulfur in hair proteins and oxygen in the air to deposit a dark metallic film over time.
• Progressive Action: Darkens gradually with each application (marketed for gradual gray coverage).
• Severe Chemical Incompatibility: Applying professional hydrogen peroxide, ammonia, permanent wave solution, or hair relaxer over metallic salts triggers an immediate violent chemical reaction: the hair heats up, smokes, boils, turns green or black, and melts off at the scalp.

PA State Board Test for Metallic Salts: Mix 1 oz of 20-volume hydrogen peroxide with 20 drops of 28% ammonia. Immerse a cut strand of hair (20 strands) in the solution for 30 minutes. If metallic salts are present, the hair will lighten rapidly, boil/smoke, or disintegrate.