Olga_Rivas

Olga Rivas Chemistry Information Retrieval

=History, Chemistry, and Applications of Hair Dyes=

Introduction
Evolutionarily hair’s function is to provide thermal regulation and camouflage for humans and other animals although humans depend on clothing for warmth. The hair on one’s head serves primarily as insulation and cooling and protection from UV radiation. Although its purpose is strictly evolutionary, the meaning of hair has transformed into something much more than an insulator and protector. Hair has been a symbol of social status, power, and wisdom. Healthy hair can signify youth and health while color and texture can show ethnic ancestry [1]. While some cultures forbid cutting it and others praise long luscious locks, there are many different cultural standards around the world.

A Brief History of Hair Coloring
Evidence has been found that suggests that minerals, plants, and insects were used by man to paint on their bodies and hair as early as their existence. Around 1500 B.C. Egyptians started to use henna as a hair coloring agent [2]. They also used kohl as a dye and often wore wigs to alter hair color [3]. Throughout time, the color of one’s hair has always had significance and the meaning, depending on the era, attached to hair color has evolved. For example, to the Greeks, lighter colored hair signified innocence, high social standing, and sexual desirability. They were the first to popularize hair bleaching [4]. In the first century, the Gaul’s dyed their hair red to signify class and rank. During the dark ages, red hair was looked at as a sign of witchcraft. Before this time, there was no record of natural red hair. However, a genetic mutation gave rise to this natural red coloring in Scotland around this time. Ironically, years later red hair was thought of as a status of royalty due to Queen Elizabeth’s auburn hair. At one point, blonde hair was worn by women of the night and women used plant extracts to darken their hair to steer from this negative stereotype. During the Renaissance, however, blonde hair was admired by many due to its angelic impression. Even today, there is an attraction to the “Hollywood blonde bombshell” which is looked at as sexy in the eyes of society [2]. In 1863, Dr. August Wilhelm von Hofmann discovered the properties of para-phenylenediamine (PPD)(compound 1), a common ingredient in hair dye [3].



PPD is also used in engineering polymers and composites, aramid fibers, rubber chemicals, textiles dyes, and pigments. It has very high temperature stability, strength, and chemical and electrical resistance [5].This marked the first breakthrough in hair color science. A few years later, London chemist E.H. Thiellay and hairdresser Leon Hugot created an alternative for lightening hair by using hydrogen peroxide instead of alkaline solutions [3]. The first patent about the use of PPD was established in 1883 by Monnet [6]. In 1948, Eugene Schueller, a French chemist, patented the first hair dye cream made from oxidation dye base consisting of phenylamines, phenylenediamines, phenols, and amino phenols and a sulfhydrl compound made from ionizable inorganic salts to slow oxidation and extend the shelf life of the product [7]. In 1953, Wella developed the first permanent cream hair colorant which was a less messy way to color hair. Demi-permanent hair color showed up in the early 1980’s. In 2003, scientist discovered a method to reduce damage of the by due to the HO radical and increase color uptake by using a chelant, ethylenediaminedisuccinic acid (EDDS)(compound 2), to the formula. In 2007, a new bleach engine was discovered that reduces the hair fiber and f-layer damage and cuts the coloring time down to ten minutes [3].

The Biological and Chemical Structure of Hair
To understand the mechanism of how hair dye works, the structure of the hair must be explored. Hair is made up of a protein called keratin surrounded by a sulfur matrix protected by overlapping scales [3]. Keratin is composed of a complex mixture of proteins. These include, keratins, KFAPs and epithelia enzymes. There are many different types of keratin in the body; the keratin produced in the suprabasal cell in the skin differs from that of the hair cortex and cuticle and fingernails. The hair has a complex expression pattern of keratins. The outer root sheath contains cytokeratins K5 and K14 while the hair shaft contains nine type I and six type II hair keratins [8]. There are two parts to hair, the bulb and the shaft. The bulb, housed in the follicle, is the biologically active site where new growth is made while the shaft is the visible part. When new cells are formed from the bulb and are pushed up through the follicle, where they harden and obtain their color. There are three layers to the hair shaft: the cuticle, cortex, and medulla. The cuticle is composed of colorless cells thatare packed very tight together and overlapped like scales. The cortex provides supports the physical and mechanical properties of the hair such as hair strength and texture. This is also where the color pigments are stored. This middle layer is made of millions of polypeptide chains crossed linked by 3 types of side bonds: hydrogen, salt, and disulfide [9]. Lastly, the medulla is a hollow core inside the hair. Natural hair color is determined by the color pigments known as melanin within the cortex. There are two flavors of melanin, phaeomelanin which give rise to dark hair colors such as black and brown and eomelanin which give rise to light hair colors such as blonde and red. Eumelanin is a polymeric pigment made from 5,6-dihydroxyindole(compound 3) derived from tyrosine. Upon oxidation by hydrogen peroxide or potassium permanganate, eumelanin converts to a mixture of pyrrole carboxylic acids. Pheomelanin, unlike eumelanin, contains considerable sulfur content. They are also more stable toward bleaching than eumelanins[10]. The absence of these hair pigments creates gray hair[3]. So in order to alter one’s hair color, a dye must penetrate the cuticle and deposit/remove color in the cortex.

Various Types of Hair Dyes
There are several types of hair dyes: bleaching and highlights, temporary, semi-permanent, permanent, and ammonia-free hair dye. Bleaching utilizes oxidation in order to remove the color from the hair. Bleaches typically contain up to 12% hydrogen peroxide which is usually active at basic pH but it is usually stored in acidic solution. Right before use, it must be mixed with an alkali-containing base to change the pH of the bleach to approximately 10, this usually being ammonia. The pH is typically controlled by metasilicates mixed with persulfates and ammonia salts [11]. If all of the color pigments were bleached, the hair would appear a pale yellow due to the natural pale yellow color of keratin [12]. In order to obtain the “peroxide blonde” look, the hair is treated with a toner, a dilute solution of dyes, after the bleaching is complete. There are 2 steps in the mechanism of bleaching. The first step is a fast dissolution step of peroxide where the eumelanin granules disperse and dissolve. The second step is a slower decoloration step. The chemical process of the decoloration is still unknown, however, it is suggested that the dissolution involves the destruction of the cross-links within eumelanin and the decoloration involves a more involved breakdown of the polymeric structure [11]. Temporary dyes are acidic dyes that do not significantly penetrate the hair shaft and can be washed off with shampoo. Because these dyes do not penetrate the hair to alter the pigments within the cortex, they work by altering the way light reflects off the cuticle[13]. Semi-permanent hair dyes, also known as direct hair dyes, are temporary hair dyes that are easier to use and give a more natural look than permanent hair dyes. Because these do not contain bleach, they cannot lighten hair color [12]. These dyes contain small molecules that are small enough to enter the cortex without damaging or greatly altering the scales of the cuticle. Semi-permanent dyes, like temporary dyes, can be shampooed out but unlike temporary dyes they last through several washes[13].

Oxidation Dyes
Permanent hair dye, also known as oxidation dyes contain an oxidizers, usually hydrogen peroxide, and ammonia that is mixed with the coloring agent right before it is applied to the hair [14]. Permanent dyes can be further divided into oxidation and progressive hair dyes [12]. Progressive dyes use metallic salts such as lead acetate as a color additive. This active ingredient oxidizes to create the dark colored compounds when exposed to air [13]. Progressive dyes change light colored hair almost black by reacting sulfur with the keratin and oxidizing the hair surface [12]. Ammonia free hair dyes are made of monoethanolamine (MEA)(compound 4) which is doubly functionalized as a primary amine and a primary alcohol. It is used in place of the ammonia of other dyes. Using this is beneficial because it is less volatile and less damaging to the hair than ammonia [14]. Oxidation dyes come as a two-component kit. The first component contains a solution of dye intermediates such as PPD, which will form the dye after it has reacted, and preformed dyes. The second component contains an oxidizing agent, known as the developer, which is typically a solution of hydrogen peroxide (usually 6%). The dye solution and the hydrogen peroxide are mixed together just before application. Upon application the hair will swell, opening the cuticle, allowing the intermediate dyes and the preformed dyes to penetrate into the cortex before they completely react. The dye intermediates must enter the cortex before they react because once reacted, the molecules are too large to enter the cortex. In the cortex, it will react with the hydrogen peroxide and other dyes to form colored dimers, trimers, and large molecules that give rise to the color components that give the hair its dyed color[12]. Because of the increase in molecule size, they will not be able to escape the cortex and will not wash out. The hydrogen peroxide not only initiates polymerization of the dye molecules but it also bleaches the melanin particles within the hair. This allows dark hair to be dyed lighter colors. Another important component in permanent hair dye is an alkaline material, usually ammonia. This is what raises the cuticle scales to allow the dye molecules to penetrate the hair easily. This alkaline pH is needed to allow the hydrogen peroxide to produce oxygen. To prevent the ammonia from reacting with hydrogen peroxide too early, it is included in the dye solution component. Varying the pH of the combined hair dye solutions can change the reactions rates of the polymerization of the dye molecules which can influence the shade of the color produced[13]. Primary intermediates, or bases, such as PPD are dyes that react with themselves to form colors [11]. These typically are para-diamines or para-aminophenols which when oxidized produce colored products [6]. These can be combined with other primary intermediates to form all different kinds of colors. Couplers, or color modifier, can also be added to bases to produce colors but are inactive without the bases [11]. These couplers are typically meta-diamines, meta-aminophenols and mono or polyhydric phenols [6]. Table 1 shows the frequently used bases in hair dyes and the colors they produce. Table 2 shows the frequently used couplers and the colors they produce.

Table 1
(information found in source 11)
 * Base || Color on hair ||
 * p-Phenylenediamine || Dark brown/black ||
 * 2,5-Diaminotoluene || Reddish brown ||
 * 2-Chloro-p-phenylenediamine || Dark gray/black ||
 * N-Phenyl-p-phenylenediamine || Dark gray/black ||
 * N,N-Bis (2-hydroxyethyl)-p-phenylenediamine || Brown ||
 * 3-Methyl-4-aminophenol || Brown ||
 * 2-hydroxyethyl-p-phenylenediamine || Brown ||
 * p-Aminophenol || Light auburn ||
 * N-Methyl-p-aminophenol || Pale blonde ||

Table 2
(information found in source 11)
 * Coupler || Color on hair with base ||
 * Resorcinol || (A)greenish brown; (C)yellow-gray ||
 * 4-Chlororesorcinol || (A)greenish brown ||
 * 2-Methylresorcinol || (A)yellow brown; (C)gray-violet ||
 * 1-Naphthol || (A)purple; (B)blue ||
 * 2-Methyl-1-naphthol || (A)blue-violet; (C)red ||
 * 1,5-Dihydroxynaphthlene || (A)blue-gray ||
 * 1,7-Dihydroxynaphthalene || (A)violet ||
 * m-Aminophenol || (A)magenta/brown ||
 * 4-Amino-2-hydroxytoluene || (A)magenta; (C)orange-red ||
 * 5-(2-Hydroxyethyl)amino-2-methylphenol || (C)orange-red ||
 * m-Phenylenediamine || (A)blue; (B)green-blue ||
 * 2,4-Diaminophenoxyethanol || (A)violet-blue; (C)dark red ||
 * 2,6-Diaminopyridine || (A)blue ||
 * (A)=p-Phenyldiamine; (B)=N,N-Bis(2-hydroxyethyl)-p-phenylenediamine; (C)=p-Aminophenol ||

The general mechanism by which oxidative dyes works is as follows: the base is oxidized to a reactive imine then attacks electrophilic sites on the color couplers to produce a diphenylamine derivative. This product is then oxidized to the indo dye, the basic chromophoric unit of the dye system[11].

Health Risks
Although a popular trend though the past 60 years, dying hair has many risks associated with it. Hair color products are known to contain mutagenic and carcinogenic compounds in animals. Two case-control studies have been done that suggest the use of hair dyes can increase a person’s risk of leukemia and non-Hodgkin’s lymphoma. In a study performed to determine if these risks were legitimate. Upon further investigation, hair dye use was associated with odd ratios of 1.5 for non-Hodgkin’s lymphoma, 1.7 for Hodgkin’s disease, 18 for multiple myeloma, and 1.0 for chronic lymphocytic leukemia. The risks associated with permanent hair dye usage were found to be greater than that of semi-permanent hair dye. In addition, long duration and early age use also increased risk. In conclusion, the use of hair dye increased the risk of non-Hodgkin’s lymphoma[15]. In 1975, the Ames assay using Salmonella typhirmurium found that a number of hair dye ingredients were mutagenic. This was then followed by the discover of a carcinogenic effect due to some dye intermediates by the National Cancer Institute [6]. In the mid-1970s, manufacturers changed their original formulas due to the findings that some of the ingredients such as aromatic amines caused cancer in animals. There have also be controversial results on whether certain compounds cause breast and bladder cancers[16].

Natural and Safer Alternatives to Harsh Chemical Dyes
Due to all of the controversy of health risks due to chemical hair dyes, many people have turned to safer alternatives. Many vegetables are being used as starting materials to produce ”green” hair dyes. However, some complications arise from using these alternatives; they typically require longer exposition times and higher temperatures. Plants often contain low concentrations of these natural pigments and are usually impure and have poor solubility. In a study done to test the different effects of multiple pigments of vegetal origin the following conclusions were made; red pigments were successfully achieved from alizarin(compound 5) extracted from rose madder and blue pigments were successfully achieve from anthocyanin (compound 6) extracted from mulberry fruits [17]. Another method of coloring hair is using turmeric to add a yellow color of great range from wheat tones to banana yellow colors depending on the concentration of the paste made from turmeric powder. Creating a tea from beets and water can be used to add bright pink or red to light hair. For a brighter effect, a beet emulsion can be used[18]. A popular alternative to harsh chemical dyes is using henna. Henna has been used in cosmetics for 6,000 years. There have been reports that mummies of Ancient Egypt used henna to dyed hair bright red. It spread to Europe in the 1800s as an aesthetic movement. As a tradition of the Prophet Muhammad, Muslim men have been known to dye their hair using henna. Even now henna is available for hair dye in many countries. Unlike oxidative dyes, the color of the hair after dying with henna is dependent on the original color of the hair and the quality of henna used. The colors can range from orange to auburn to burgundy. Often products sold as “henna” are actually a mixture of henna and other natural hair dyes or metal salts or oils or waxes[19]. The compound within henna that is responsible for its coloring capabilities is lawsone (hennotannic acid or 2-hydroxy-1,4-naphthaquinone)(compound 7) in the leaves [20].

Conclusion
Although some are opposed to the use of harsh chemical dyes and turn to the safer alternatives, the hair coloring industry is growing greatly. Ever since its discovery in the late 1800s and early 1900s, scientist have been working on improving formulas to last longer, to decrease processing time while applied, to ease applications, and many more improvements suggested by customers. In addition, cosmetic companies have also been creating other products to accompany their hair coloring products. These are things such as shampoos that help to protect color treated hair. Some of these actually include the bases and couplers of the hair dye to help replace some lost color while some simply help keep color particles from escape the hair. Some companies have also created thermal heat protectants, conditioners, leave in conditioners, and many other creations specifically for color treated hair. As explained the hair color science is only going to get larger and further developed from here on out.

References [1] Hair. In Wikipedia. [|Link] [2] History of haircolor. [|Link] [3] Kenneally, D. Hair color reseach update. [|Link] [4] Turk, R. 1995, Jan 12. A brief history of hair : Dyeing. bleaching. coating with lard! what some women through the years have done--and will do--for a 'do. [|Link] [5] DuPont. p-phenylenediamine (ppd).[| Link] [6] Corbett, J. (1999). An historical review of the use of dye precursors in the formulation of commercial oxidation hair dyes. Dyes and Pigments, 41(1-2), 127-136. [|Link] [7] Schueller, E. Hair-dye Compositions. L'Oreal Soc, assignee. Patent 2610941. 16 Sept. 1952. [|Link]. [8] Porter, R., Gandhi, M., Wilson, N., Wood, P., McLean, W., & Lane, E. (2003). Functional analysis of keratin components in the mouse hair follicle inner root sheath. British Journal of Dermatology, 150(2), 195-204. [|Link] [9] Bragulla, H., & Homberger, D. (2009). Structure and functions of keratin proteins in simple, stratified, keratinized and cornified epithelia. Journal of Anatomy, 214(4), 516-559. [|Link] [10] Brown, K. 2000, June 08. Hair coloring. [|Link] [11] Exposure to reactants and reaction products of oxidative hair dye formulations. 2005, Dec 13.[|Link] [12] Hair dye products. 1997, Nov 01. [|Link] [13] Forbes, N., Galley, E., & Sheard, C. 2010, March 30.Oxidative hair dyes and related topical compositions. [|Link] [14] Oliver, D. 05, Nov 2013. A brief guide to hair dye: Semi-permanent vs. permanent vs. bleach.[|Link] [15] Zahm, S., Weisenburger, D., Babbitt, P., Saal, R., Vaught, J., & Blair, A. Use of hair coloring products and the risk of lymphoma, multiple myeloma, and chronic lymphocytic leukemia. American Journal of Public Health July 1992: Vol. 82, No. 7, pp. 990-997.[|Link] [16] Nation Cancer Institute. (2011, Aug 10). Hair dyes and cancer risk. [|Link] [17] Boga, C., Delpivo, C., Ballarin, B., Morigi, M., Galli, S., Micheletti, G., & Tozzi, S. (2013). Investigation of the dyeing power of some organic natural compounds for a green approach to hair dyeing. Dyes and Pigments, 97(1), 9-18. [|Link] [18] Danielle. 2012, Sept 19. Dye your hair pretty much any color with specially brewed DIY tea.[|Link] [19] Henna. In Wikipedia. [|Link] [20] Abulyazid, I., Mahdy, M., & Ahmed, R. (2013). Biochemical study of the effect of henna(lawsonia inermis) on escherichia coli. Arabian Journal of Chemistry, 6(3), 265-273. [|Link] All images retrieved from ChemSpider

END