The dyeing of hair is an ancient art that involves treatment of the hair with various chemical compounds, with Assyrian herbals dating back to ancient times containing some of the oldest recipes for cosmetic preparations known. The ancient Egyptian Ebers Papyrus, dating to the 16th century BCE, has recipes for dyeing gray hair and eyebrows, while Assyrian clay tablets dated to the 7th century BCE mention using the gall of a black ox, cypress oil, licorice, and honey to turn gray hair black. In ancient times, the dyes were frequently obtained from plants, with some of the most well known being henna, indigo dye, Cassia obovata, senna, turmeric, and amla. Others include katam, black walnut hulls, red ochre, and leeks. Diodorus Siculus, a Greek historian, described in detail how Celtic people dyed their hair blonde, noting that their aspect was terrifying and they were very tall in stature with rippling muscles under clear white skin. Their hair was blond, but not naturally so, as they bleached it, to this day, artificially, washing it in lime and combing it back from their foreheads. They looked like wood-demons, their hair thick and shaggy like a horse's mane, with some of them being clean-shaven, but others, especially those of high rank, shaving their cheeks but leaving a moustache that covered the whole mouth. Hair coloring recipes were common in the medieval period and Renaissance, with Trotula's De ornatu mulierum, from the 12th century, having multiple recipes for bleaching and coloring hair. In the 1661 book Eighteen Books of the Secrets of Art & Nature, various methods of coloring hair black, gold, green, red, yellow, and white are explained.
The Synthetic Revolution
In 1856, English chemist William Henry Perkin accidentally discovered the first synthetic dye, mauveine, while attempting to synthesize quinine, a treatment for malaria. His discovery marked the beginning of the synthetic dye industry and laid the groundwork for later innovations in hair dye chemistry. The development of synthetic dyes for hair is traced to the 1860s discovery of the reactivity of para-phenylenediamine with air. Eugène Schueller, the founder of L'Oréal, is recognized for creating the first synthetic hair dye in 1907. In 1947 the German cosmetics firm Schwarzkopf launched the first home color product, Poly Color. Hair dyeing is now a multibillion-dollar industry that involves the use of both plant-derived and synthetic dyes. The four most common classifications are permanent, demi-permanent, semi-permanent, and temporary. Permanent hair color generally contains ammonia and must be mixed with a developer or oxidizing agent in order to permanently change hair color. Ammonia is used in permanent hair color to open the cuticle layer so that the developer and colorants together can penetrate into the cortex. The developer, or oxidizing agent, comes in various volumes, with the higher the developer volume, the higher the lift will be of a person's natural hair pigment. Someone with dark hair wishing to achieve two or three shades lighter may need a higher developer whereas someone with lighter hair wishing to achieve darker hair will not need one as high. Timing may vary with permanent hair coloring but is typically 30 minutes or 45 minutes for those wishing to achieve maximum color change.
The Chemistry Of Color
Synthetic permanent hair coloring requires three components: 1,4-diaminobenzene historically or 2,5-diaminotoluene currently, a coupling agent, and an oxidant. The process is typically performed under basic conditions. The mechanism of oxidation dyes involves three steps: oxidation of 1,4-diaminobenzene derivative to the quinone state, reaction of this diimine with a coupler compound, and oxidation of the resulting compound to give the final dye. The preparation is in the leuco form, and oxidizing agents are usually hydrogen peroxide, and the alkaline environment is usually provided by ammonia. The combination of hydrogen peroxide and ammonia causes the natural hair to be lightened, providing a blank canvas for the dye. Ammonia opens the hair shaft pores so that the dye can actually diffuse inside the fiber. These dye intermediates and coupler compounds can undergo oxidation and coupling reaction to form high molecular weight products, which are trapped in the hair matrix and cannot be readily removed through washing. It was once believed that the dye forms in the above reaction bonds to hair permanently, but it was later shown that the main reason that this reaction imparts a permanent color on hair is that it produces larger dye molecules, which is locked inside the hair. Various combinations of primary intermediates and coupler compounds provide a spectrum of shades of hair colors. The primary intermediates are aromatic para compounds, such as 1,4-diaminobenzene or 4-aminophenol. The coupler compounds are meta-substituted derivatives of aniline, coming in three major classes based on the color that they produce when they react with the primary intermediate. Blue couplers include 1,3-diaminobenzene and its derivatives, while red couplers include phenols and naphthols, such as 3-aminophenol, 5-amino-2-methylphenol and 1-naphthol. The combination of 2,5-diaminotoluene with the coupler 3-aminophenol gives a magenta-brown dye, while the combination of 2,5-diaminotoluene with the coupler 1-naphthol gives a purple dye. Yellow-green couplers include resorcinol, 4-chlororesorcinol, and benzodioxoles, which produce broad-band absorption when they react to form dyes, allowing for more natural-looking hair colors.
The Modern Industry
Hair coloring is very popular, with 50-80% of women in the United States, Europe, and Japan having reported using hair dye. At-home coloring in the United States reached sales of $1.9 billion in 2011 and were expected to rise to $2.2 billion by 2016. All coloring techniques can be used with any type of color, and for lightening, the hair has to be bleached. Hair color was traditionally applied to the hair as one overall color, but the modern trend is to use several colors to produce streaks or gradations. These are referred to as highlighting, where sections of hair are treated with lighteners, and lowlighting, where sections of hair are treated with darker hair colors. Splashlighting is a horizontal band of bleached hair from ear to ear. There are also newer coloring techniques such as ombré, shatush, balayage, and airtouch, in which hair is dark on the crown and bit by bit becomes lighter toward the ends. These are off-the-scalp techniques, and can be applied by the following methods: foiling, where pieces of foil or plastic film are used to separate the hair to be colored, employed especially when more than one color is to be applied, this method ensures that only the desired hair strands are colored, and the rest spared. Cap, when a plastic cap is placed tightly on the head and strands are pulled through with a hook, is a method infrequently practiced other than for applying highlights to short hair. Balayage, where hair color is painted directly onto sections of the hair with no foils used to keep the color contained, is a method growing in popularity due to its observed effect of appearing more natural. The difference between balayage and ombré is that a balayage requires more precise hand-painting sections of hair and typically costs more. Baby lights are very thin highlights that are created by using a fine color technique, and baby light results are very natural and subtle. Dipping or tip dyeing is where tips of the hair are dipped directly into dye. Hair coloring can also be applied on the scalp for a more solid level of coverage, with all-over color where the person wants all of their hair to be a different solid color, and root touch-up where color is applied only to the most recent section of re-growth, usually the first inch of hair nearest the scalp. Root touch-ups are repeated every 4 to 6 weeks as the natural color grows in and becomes apparent. People who color their hair to disguise gray often have root touch-ups. Block coloring is where the person wants two or more colors applied to their hair, resulting in dimension and contrast.
The Health Debate
Phenylenediamine based hair dyes have been controversial and subject of many studies, with several products having been removed from the marketplace over the past decades. Hair coloring can involve the use of chemicals capable of removing, replacing, and/or covering up pigments naturally found inside the hair shaft, and 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. According to the International Agency for Research on Cancer, in vitro and in vivo studies have shown that some hair dyes and many chemicals used in the hair dyeing process can be considered mutagenic and carcinogenic. In certain individuals, the use of hair coloring can result in allergic reactions and/or skin irritation, with individuals allergic to gluten needing to be cautious when purchasing hair color since certain hair dye includes gluten. Gluten does not need to be ingested for it to cause an allergy, and skin contact with gluten may cause a reaction, leading to an allergy. Symptoms of these reactions can include redness, sores, itching, burning sensation and discomfort, and symptoms will sometimes not be apparent immediately following the application and processing of the tint, but can also arise after hours or even a day later. To help prevent or limit allergic reactions, the majority of hair color products recommend that the client conduct a patch test before using the product, involving mixing a small quantity of tint preparation and applying it directly to the skin for a period of 48 hours. If irritation develops, manufacturers recommend that the client not use the product. European dermatologists have, however, strongly advised against such pre-use testing, as it entails additional sensitisation risk and the interpretation by lay people may not be sufficiently accurate. Skin and fingernails are made of a similar type of keratinized protein as hair, and drips, slips and extra hair tint around the hairline can result in patches of discolored skin, which is more common with darker hair colors and persons with dry absorbent skin. That is why it is recommended that latex or nitrile gloves be worn to protect the hands. This discoloration will disappear as the skin naturally renews itself and the top layer of skin is removed, typically taking a few days or at most a week. Ways of preventing skin discoloration are to wear latex or nitrile gloves to protect the hands and also by applying a thin layer of petroleum jelly or oil-based preparation around the hairline. Gentle abrasives such as moist baking soda or a small amount of toothpaste applied with a toothbrush may also help remove the uppermost layer of skin and dye. Acetone and nail polish remover are not considered effective, and laundry detergent may sometimes work as may moist cigarette ash rubbed into the stained area. The salt lead acetate, formerly the active ingredient in gradual darkening products such as Grecian formula, is toxic, and lead acetate trihydrate has also been shown to cause reproductive toxicity. Articles link the development of some forms of cancer, including leukemia, non-Hodgkin's lymphoma, bladder cancer, blood cancer, and multiple myeloma, with use of hair color. More specifically, prolonged use of permanent dark hair dyes can double a person's risk of getting some types of blood cancer. In 2004 a known human carcinogen, 4-aminobiphenyl or 4-ABP, was found in some commercial hair dyes, but evidence is limited and inconsistent for the link between cancer from hair dye. Phenylenediamine is known to cause health concerns, such as skin irritation, and exposure to phenylenediamine can occur during manufacturing or during the use of hair dyes. According to the Product Safety Summary Sheet by DuPont, Para-Phenylenediamine is labeled as toxic and can cause adverse effects on aquatic organisms and could cause long-term effects in aquatic environments. In October 2017, the leading breast surgeon Professor Kefah Mokbel published a meta-analysis showing that use of hair dyes might increase the risk of developing breast cancer by 20% among users, and another 2019 study found similar results.
The Legal And Religious Context
Hair dyes are cosmetic compounds that make contact with the skin during application, and because of this skin contact, there exists some health risk associated with use of hair dyes. Thus, hair dyes are regulated in the commercial marketplace, and as new toxicity data is generated for some hair dyes and health risks are discovered, some of these hair dyes are being legally restricted from the cosmetic marketplace. The European Union is particularly stringent with regard to health regulations, and to ensure that hair dyes contain only safe substances, the European Commission adopted the Directive 2012/21/EU to restrict the use of around 45 chemicals in hair dyes. The directive on dyes is part of a general and comprehensive set of regulations, the EU Cosmetics Directive 76/768/EC. For Muslims, if a man is not of advanced age, there is no harm in his using black dye, and some of the early Muslims, including some sahabah, permitted the use of black dye. As narrated in a hadith, the best thing with which to dye gray hair is henna and katam, a plant from Yemen which colors it black tinged with red. Alternative hair coloring products are designed to create hair colors not typically found in nature, and these are also referred to as vivid color in the hairstyling industry. The available colors are diverse, such as the colors green and fuchsia, and permanent alternatives in some colors are available. More recently, blacklight-reactive hair dyes have been brought to market that fluoresce under blacklights, such as those often used at nightclubs. The chemical formulae of alternative color dyes typically contain only tint and have no developer, meaning that they will only create the bright color of the packet if they are applied to light blond hair. Darker hair, medium brown to black, would need to be bleached in order for these pigment applications to take to the hair desirably. Some types of fair hair may also take vivid colors more fully after bleaching. Gold, yellow and orange undertones in hair that has not been lightened enough can muddy the final hair color, especially with pink, blue and green dyes. Although some alternative colors are semi-permanent, such as blue and purple, it could take several months to fully wash the color from bleached or pre-lightened hair. In 2018, a system for making semi-permanent hair dyes from renewable waste blackcurrant fruit skins from the fruit pressing industry was developed, with anthocyanin pigments extracted from the blackcurrant skin waste and formulated into hair dyes. The dyes showed high buildup on hair and gave an intense blue color, which was stable to multiple washes. Temporary hair color is available in various forms including rinses, shampoos, gels, sprays, and foams, and is typically brighter and more vibrant than semi-permanent and permanent hair color. It is most often used to color hair for special occasions such as Christmas and Halloween costume parties. The pigments in temporary hair color cannot penetrate the cuticle layer of the hair, and the color particles remain adsorbed to the surface of the hair shaft and are easily removed with a single shampooing. Temporary hair color can persist on hair that is excessively dry or damaged in a way that allows for migration of the pigment to the interior of the hair shaft. Some plants can be used for temporary coloring, too, such as beet juice.