Lecture 12

Hair dyes

• The principle of artificial hair dyeing• Factors affecting artificial hair dyeing• The different types of hair dye• Hair dye precautions

The principle of artificial hair dyeing

• The natural hair colour is due to colouring pigments localized in the cortex and seen through the transparent cuticle layer, which gives the hair its natural lustre.

• A good hair dye formulation should simulate the natural hair colouration, i.e. the dye molecule should be allowed to cross the cuticle through the pores and lodge in the cortex, where they bind to keratin

• Hair coloring is the practice of changing the color of hair.

• The main reasons for this practice are cosmetic (e.g., to cover gray hair, to change to a color regarded as more fashionable or desirable, or to restore the original hair color after it has been discolored by hairdressing processes or sun bleaching).

• Hair dyeing, which is an ancient art, involves treatment of the hair with various chemical compounds.

Factors affecting artificial hair dyeing

• The molecular size of the dye• The size of the pores of the cuticle Average diameter of pore in the dry state ≈ 0.5 nm, It increases 8 folds upon wetting to ≈ 4 nm

Types of hair dyes

Hair dyes can be divided into three general categories:

1. Temporary hair dyes2. Permanent hair dyes3. Semi-permanent hair dyes

1. Temporary hair dye

• Coats the outside of the hair. Uses large molecules too big to penetrate the hair shaft.• There is a physical action (coating) on the hair, not chemical action (penetrating).• Does not change the structure of the hair.

• Temporary color formulations are of the ‘‘leave-on’’ type, which means that they are applied to hair usually after shampooing and left there to dry.

• Temporary hair color is available in various forms including rinses, shampoos, gels, sprays, and foams.

• It is most often used to color hair for special occasions such as costume parties

• Exposing the coloured hair to heat (e.g. from a blow dryer) may bring about some increase in durability of the imparted colour to shampooing.

• The main disadvantage to using temporary dyes is that they will likely wash out the next time you shampoo.

• The color vehicles in these dyes are mostly water, organic solvents, surfactants and conditioning agents and therefore do less damage to the hair when used.

Temporary hair dyes are the least hazardous of all dyes.

Examples

• Chamomile: (a natural dye) is a yellow dye stuff• Azo dyes: (a synthetic dye) approved colours producing all shades from

yellow to black

2- Permanent hair dyes

Permanent hair dyes are divided into two types:

I. Oxidation hair dyesII. Progressive hair dyes.

Oxidation hair dyes (Para-dyes)

• Oxidation hair dyes tend to be the most popular dyes on the market today.

• These products will have the most long-lasting results, given that the dye fully penetrates the hair shaft.

• Although the colour may fade and new roots will grow in, the permanent dye will remain in the hair until it is trimmed away.

• Permanent dyes use chemicals that strip the hair of its natural color and replace it with another color—a permanent dye.

Oxidation hair dye

• These hair colors have the smallest molecule which makes it easier for them to penetrate the hair shaft and the scalp.

• This process has the greatest impact on the hair structure, which is permanently changed

• These dyes are available in a variety of forms e.g., lotions, gels, shampoos, and creams

• Most often, the colourant is supplied as a two-component kit consisting of a mixture of dye precursor and of a stabilized solution of hydrogen peroxide.

• The two components are mixed immediately before use, applied to hair, and left for 20 to 40 minutes before being rinsed out with water.

• The color formation commences upon mixing and involves complex reactions between precursors and the oxidant

Formulation

• dye intermediate• modifiers• developer • alkalinizers• antioxidants • fragrance

dye intermediate

• It is the basic constituent of these dyes • These are solutions of easily oxidizable compounds, e.g. para and ortho-substituted aminophenol and phenylenediamines

• Upon oxidation by peroxide these compounds form coloured quinone imines paraphenylenediamine

Modifiers (Couplers)

• These are already dyes that are added to achieve the intended shades, in an aqueous, ammoniacal vehicle

• These are less easily oxidizable m-substituted amino acid/or phenolic compounds

e.g. m- phenylenediamine, m-aminophenol and resorcinol • The modifier condenses with the imines to yield the final dye molecules. Resorcinol

Developer

• a solution of hydrogen peroxide, usually 6%, in water or a cream lotion.

• The ammoniacal dye solution and the hydrogen peroxide solution are mixed shortly before application to the hair.

• Whereas the colour-forming reactions take place in the dye mixture, a significant fraction of the dye precursors diffuse rapidly into the hair together with the hydrogen peroxide forming the colorant moieties throughout the hair fiber.

• The process is carried out at alkaline pH, which also favors the bleaching of the melanin pigment by H2O2.

Alkalinizers

• Alkalinizers are added to change the pH of the dye formula, because the dyes work best in a highly alkaline pH.

• Ammonium hydroxide is a common alkalinizer, it affects the disulphide linkage and causes swelling of the hair, which enhances dye penetration

Antioxidants

Antioxidants protect the dye from oxidizing with air during storage

- Most commonly used is sodium sulfite.

An alkaline reaction causes the cuticle toswell, allowing hydrogen peroxide and dyeto enter.• The hydrogen peroxide“oxidizes” the melanin, and lightens the colour.• The hydrogen peroxide also causes the dye to “develop” and “deposit” colour.• A neutral or slightly acid after-rinse stopsthe alkaline reaction, allows the cuticle toclose, and traps the colour molecules inside.

Although permanent hair dyes are the most long-lasting, they are also the most threatening to the health of your hair.

Over processing from permanent dye can lead to breakage due to excessive dryness

Allergic reaction to p-phenylenediamine

• It is reported that severe allergies to paraphenylenediamine caused Germany, France and Sweden to ban its use in their countries.

• If you develop itching, hair loss or a burning sensation within 10 days after initial use, stop using the dye and seek testing from an allergist

According to the FDA, a warning must appear on the label as follows:

Caution - This product contains ingredients which may cause skin irritation on certain individuals and a preliminary test according to accompanying directions should first be made.

This product must not be used for dyeing the eyelashes or eyebrows; to do may cause blindness.

Notes on oxidation hair dyes

• The shades obtained depend on the type and number of oxidation bases and modifiers

• They cover grey hair more efficiently than other dyes• Lighter hair colours can be obtained• A conditioner must be applied after using oxidation

dyes

Time Frame The timing of colouring your hair is important. It is best to wait at least 6 weeks in between treatments to

allow the scalp and roots to heal completely from the irritation that causes redness or itchiness

II. Progressive hair dye

• Progressive hair dye products contain lead acetate as the active ingredient.

• Lead acetate is approved as a colour additive for colouring hair on the scalp at concentrations not exceeding 0.6% w/v, calculated as metallic lead

• Progressive hair dyes change the color of hair gradually from light straw color to brown to almost black by reacting with the sulfur of hair keratin as well as oxidizing on the hair surface forming a mixture of insoluble sulfides and oxides imparting to the hair a darker colour

• They must be applied daily until the required shade is reached. This is then maintained by application every few days

Lead acetate in hair dye products

The FDA regulation requires that the following caution statement appear on the product labels:

• “Caution: Contains lead acetate. For external use only. Keep this product out of children’s reach.

• Do not use on cut or abraded scalp. If skin irritation develops, discontinue use.

• Do not use to colour mustaches, eyelashes, eyebrows, or hair on parts of the body other than the scalp.

• Do not get in eyes. • Follow instructions carefully and wash hands thoroughly after

use”

3. Semi-permanent dye

The difference between a permanent dye and Semi-permanent dye is that the latter does not require a developer.

This would mean that the liquid, gel or aerosol foams can be directly applied to the hair without any prior mixing.

• The majority of products’ features a blend of low- and medium-molecular weight dyes that are capable of penetrating into the hair shaft .

A blend is necessary to achieve the desired color• These dyes penetrate the hair shaft, but not as deeply as

permanent dyes. • They produce a direct dyeing (no chemical reaction) by

penetrating the cuticle when the hair is wet( or treated with a swelling agent) and become locked after drying.

• usually wash out within six to ten shampoos.

• Semi-permanent dyes usually come as liquid, gel or aerosol foam solutions.

• In all cases, the dyes are dissolved or dispersed in a detergent base that contains a thickener so the product stays on the hair without running or dripping.

• With most of these dyes, your hair will be washed and then the product applies.

• After waiting about 20-40 minutes, the dye will be worked into your hair and then rinse it off with water and frequently followed by a conventional shampoo

The dyes that are used are generally nitrophenylenediamines (deep yellow) and nitroaminophenols e.g. picric acid (deep orange red)

Picric acid

• Often included in the semi- permanent category is Henna• Henna is the only vegetable dye that is permitted to be used in

the United States• Henna consists of the dried leaves of the plant Lawsonia alba The active ingredient, lawsone (2-hydroxy-l-4-naphtoquinone)• Using henna, only limited reddish shades can be achieved.• In some products, henna is mixed with other dyes to obtain

more variety in colour.

Hair dye precautions

• The less hair dye you use over a lifetime, the less likely you will be exposed to enough dye to cause cancer

• Delay dyeing your hair until later in life when it is really needed

• Consider using henna , which is largely plant derived, or hair dyes that are lead acetate –based.

• Don’t leave the dye on your head longer than necessary

• Rinse your scalp thoroughly with water after use• Wear gloves when applying hair dye• Carefully follow the direction in the hair dye package• Never mix different hair dye products, potentially harmful

reactions can be induced• Be sure to do a patch test for allergic reactions before applying

the dye to your hair• Never dye your eyebrows or eyelashes. An allergic reaction to

dye could prompt swelling, inflammation and susceptibility to infection in the eye area

Adverse effects of hair coloringHair coloring involves the use of chemicals capable of removing, replacing and/or covering up pigments naturally found inside the hair shaft. Use of these chemicals can result in a range of adverse effects, including temporary skin irritation and allergy, hair breakage, skin discoloration and unexpected hair color results. Side effects of various products result in loss of hair and in extreme cases baldingIf consumed by the body by means of inhalation or digestion certain hair dye brands have shown evidence of causing constipation and other dangerous disruptions within human organs.