Hair dye works by either coating the hair shaft (temporary dyes) or penetrating the hair and chemically altering its natural pigment (permanent and semi-permanent dyes).
The Process of Permanent Hair Dye
Permanent hair dye involves a multi-step process:
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Cuticle Lifting: An alkaline ingredient, such as ammonia or monoethanolamine, swells the hair's outer layer (cuticle), opening pathways for the dye to penetrate. This is described in the C&EN Global Enterprise article: "The alkaline ingredient, usually ammonia or monoethanolamine, gets the color into the hair by swelling the outer hair layer, or cuticle."
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Melanin Oxidation: Hydrogen peroxide, a key component of most permanent dyes, oxidizes melanin, the hair's natural pigment, rendering it colorless. This process is mentioned in the reference from May 4, 2020: "Once in the cortex, hydrogen peroxide plays its second role: oxidizing melanin, the hair's natural color molecule, to render it colorless."
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Dye Molecule Penetration: The dye molecules, now able to access the hair's cortex (middle layer), bind to the keratin proteins within the hair shaft. The May 4, 2020, source explains this: "Openings in the cuticle allow the dye molecules and hydrogen peroxide to enter the hair's middle layer, or cortex. The bulky dye molecules stay wedged in to provide lasting color."
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Color Deposition: The dye molecules deposit color, replacing the oxidized melanin. The dye's color is determined by the specific dye molecules used.
Types of Hair Dye
There are various types of hair dye, each working differently:
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Permanent: These dyes chemically alter the hair's natural pigment, resulting in long-lasting color. They require a developer (usually hydrogen peroxide) to lift the cuticle and oxidize melanin.
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Semi-permanent: These dyes coat the hair shaft and deposit color without significantly altering the natural pigment. The color fades gradually with washing.
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Temporary: These dyes only coat the hair's surface and are easily washed out. One source describes these as: "Some hair dyes are basically fine-grained paint."
Understanding Blonde Hair Dye
Achieving blonde hair often involves bleaching first, as mentioned in a Reddit post: "The best way to do that is to bleach it with regular powder bleach and developer. It can lift your hair slightly, so would a high lift color." Bleaching lifts the natural pigment to allow for lighter colors to be applied subsequently.
