Hair dye
Hair coloring products generally fall into four categories: temporary, semipermanent, deposit only/demi, and permanent. All these hair color products, except for temporary color, require a patch test before application to determine if the client is allergic to the product.
"Hair lightening", often referred to as "bleaching" or "decolorizing," is a chemical process involving the diffusion of the natural color pigment or artificial color from the hair. This process is central to both permanent haircolor and hair lighteners.
All permanent haircolor products and lighteners contain both a developer, or oxidizing agent, and an alkalizing ingredient as part of their ammonia or an ammonia substitute. The purpose of this is to:
- raise the cuticle of the hair fiber so the tint can penetrate
- facilitate the formation of tints within the hair fiber
- bring about the lightening action of peroxide
When the tint containing the alkalizing ingredient is combined with the developer (usually hydrogen peroxide), the peroxide becomes alkaline and diffuses, or breaks up, through the hair fiber, entering the cortex, where the melanin is located. The lightening occurs when the alkaline peroxide breaks up the melanin and replaces it with new color.
Temporary
For individuals who wish to use a subtle neutralizer for yellowing hair or to neutralize unwanted tones. The pigment molecules in temporary hair color are large and, therefore, don't penetrate the cuticle layer, allowing only a coating action that may be removed by shampooing.
Semipermanent
Formulated to last through several shampoos, depending on the hair's porosity (ability to absorb moisture). The pigment molecules are small enough to partially penetrate the hair shaft and stain the cuticle layer.
Demipermanent
Formulated to deposit but not lighten hair color. Its smaller than tint molecules and therefore is able to penetrate the hair shaft.
Permanent
This is mixed with developer and remains in the hair shaft until new growth of hair occurs. It's used to match, lighten, and cover gray hair. Permanent hair color generally contain ammonia, oxidative tints, and peroxide. The allergic reaction that comes from hair dye is generally one of sensitization to PPD. The reaction will most likely occur each time one dyes their hair and probably get worse each time. The sensitization from the ingredients in hair colour can extend to sensitization of other products of same or similar composition, including but not limited to, the dye used in textiles, sunscreen, rubber, and/or certain medications.
Henna is a deposit-only hair color whose active component, lawsone, binds to keratin and is therefore permanent. It is often mixed with other plant dyes, such as indigo, turmeric, and senna, to change the color. Allergy to henna is much rarer than allergy to permanent hair colors.
Special effects
Special effects includes highlighting and "non-human" hair colors. Highlighting can range from temporary to permanent, using the techniques listed above and a special application process. The techniques required to apply highlighting can be difficult for an individual to perform upon him or herself.
"Non-human" coloring typically contains only the tinting aspect and no developer. These are typically available in punk-themed stores (such as comic book and music stores) and are rarely available at commercial hair dressers. Colors range from dark blue to hot pink and anything inbetween. Individuals with darker hair may require harsh bleaching prior to tint application. As these dyes are less permanent, users should anticipate staining of light-colored pillows for a week after application.
See also: Human physical appearance
