Definition
Hair dyes are formulations designed to impart color to hair, either temporarily or permanently.
Formulation Goals
Effective Color Change: Ability to impart lasting and even hair color.
Compatibility: Minimal damage to hair fibers and scalp.
Oxidative Stability: For permanent dyes, proper oxidation processes are essential.
Safety: Reduced allergenic and toxic potential.
Types of Hair Dyes
Permanent Dyes: Typically use oxidative chemistry.
Semi-Permanent and Temporary Dyes: Generally, use direct dyes that coat the hair shaft.
Key Ingredients:
Colorants: Temporary (e.g., direct dyes) or permanent (e.g., para-phenylenediamine).
Oxidizing Agents: Activate permanent dyes (e.g., hydrogen peroxide).
Conditioners: Protect hair during dyeing (e.g., cationic surfactants).
pH Adjusters: Facilitate dye uptake (e.g., ammonia).
Processing/Preparation Methods
Mixing of Components:
Typically, hair dyes come in two parts: a colorant (containing dye precursors and couplers) and an oxidizer (usually hydrogen peroxide). Both must be stored separately until use.
Preparation Prior to Application:
The two components are mixed in a defined ratio (commonly 1:1). The mixing initiates the oxidation process.
Application:
The freshly mixed dye is applied evenly on pre-washed, towel-dried hair.
Processing Time:
Allow the mixture to act for a specific duration (usually 30–45 minutes) to ensure full color development.
Rinsing and Post-Treatment:
Thorough rinsing is required to remove residual chemicals. Conditioning treatments help restore moisture.