Cosmetics ! How does coloring dye works on my hair?

Few people would whip out a chemistry set, uncork the vials, and slap the compounds on their face. Yet, millions of women and girls essentially do that every day when they unzip their makeup bags and apply lipstick, mascara, and other makeup. Like the compounds in a chemistry set, makeup consists of chemicals. Although the chemicals in cosmetic products are intended to improve the appearance of skin, lips,hair and lashes, some can cause adverse effects.

Brushing up on makeup chemistry isn't hard: If you can read a label, you are halfway there. The U.S. Food and Drug Administration (FDA) requires cosmetics manufacturers to put labels on makeup listing ingredients in descending order of weight. Ingredients that make up less than 1 percent of the makeup item, such as fragrance or colorants, are listed after other ingredients, not in descending order of weight.

The first lesson in cosmetic chemistry is that most makeup ingredients are intended to give the product its color and consistency. A few basic classes of ingredients—coloring agents, bases, bulking agents, sunscreens, and additives—are common to many kinds of makeup.

Origin of hair dye

Various types of colors caused by hair dyes

The first safe commercial haircolor was created in 1909 by French chemist Eugene Schuller, using the chemical paraphenylenediamine. Hair coloring is very popular today, with over 75% of women coloring their hair and a growing percentage of men following suit. How does haircolor work? It's the result of a series of chemical reactions between the molecules in hair, pigments, as well as peroxide and ammonia, if present.

        Hair is mainly keratin, the same protein found in skin and fingernails. The natural color of hair depends on the ratio and quantities of two other proteins, eumelanin and phaeomelanin. Eumelanin is responsible for brown to black hair shades while phaeomelanin is responsible for golden blond, ginger, and red colors. The absence of either type of melanin produces white/gray hair.

                                  Couplers are chemical compounds that define the color of the hair dye. Shown here are three red couplers (A,B,C), two yellow-green couplers (D,E) and a blue coupler (F).

Types of hair color

The hair color an be divided into two types:

• Temporary hair color 
• Permanent hair color

Temporary hair color

Temporary or semi-permanent haircolors may deposit acidic dyes onto the outside of the hair shaft or may consist of small pigment molecules that can slip inside the hair shaft, using a small amount of peroxide or none at all. In some cases, a collection of several colorant molecules enter the hair to form a larger complex inside the hair shaft. Shampooing will eventually dislodge temporary hair color. These products don't contain ammonia, meaning the hair shaft isn't opened up during processing and the hair's natural color is retained once the product washes out. This kind of hair color will disappear as soon as the effect of dye lose.

Permanent hair color

The outer layer of the hair shaft, its cuticle, must be opened before permanent color can be deposited into the hair. Once the cuticle is open, the dye reacts with the inner portion of the hair, the cortex, to deposit or remove the color. Most permanent hair colors use a two-step process (usually occurring simultaneously) which first removes the original color of the hair and then deposits a new color. It's essentially the same process as lightening, except a colorant is then bonded within the hair shaft. Ammonia is the alkaline chemical that opens the cuticle and allows the hair color to penetrate the cortex of the hair. It also acts as a catalyst when the permanent hair color comes together with the peroxide. Peroxide is used as the developer or oxidizing agent. The developer removes pre-existing color. Peroxide breaks chemical bonds in hair, releasing sulfur, which accounts for the characteristic odor of haircolor. As the melanin is decolorized, a new permanent color is bonded to the hair cortex. Various types of alcohols and conditioners may also be present in hair color. The conditioners close the cuticle after coloring to seal in and protect the new color. So this is the reason why some hair dyes are stay long like our original hair color.

Working of Dye on hair

The steps involved in working dye on hair are : 

Step 1:

Oxidation of  p-phenylenediamine to the quinonediimine (C6H4(NH)2)

        

Step 2:

           

The second step involves the attack of this quinonediimine on the coupler. In organic chemistry, this reaction is called electrophilic aromatic substitution

Step 3:

In the third and final step, the product from the quinonediimine-coupler reaction oxidizes to the final hair dye.

Some hair coloring products

Loreal hair coloring dye

• Loreal hair color
• Garnier
• Perfect 10