The basic chemistry of hair dyes has changed little over the last century, but what do we know about the risks of colouring our hair, and why do we do it?


Every two months Barclay Cunningham goes through a process that begins with taking an antihistamine tablet. After a few hours, she smears a thick layer of antihistamine cream across her forehead, around her ears and over her neck. Finally, she shields the area with ripped-up plastic carrier bags.

All this so she can dye her hair.

It didn't start out this bad. Cunningham coloured her hair for a decade without any problems. Then, one day, she noticed that the skin on her ears was inflamed after she'd dyed her hair. She fashioned plastic bag earmuffs and carried on colouring. But the allergic reaction persisted, so her precautions became more elaborate. Now if she dyes her hair without these measures, she gets an itchy, blistery, pus-filled rash that lasts for weeks.


Suffering for the sake of tinted tresses is not a modern-day phenomenon. Humans have dyed for thousands of years, experimenting with ever-changing, often vicious, formulas to achieve a new hair colour.

The chemical history of modern hair dyes reveals that, while they were once part of an innovative industry, progress has stalled, and today they rely on antiquated methods. But consumers are not exactly pressuring the industry to innovate. Not when they are so desperate to change their hair colour that they're willing to discreetly pick scabs from their hair, as Cunningham does, for weeks after colouring.

Aesthetic tendencies drift with marketing and cultural currents, but our drive to alter ourselves is a constant. As anthropologist Harry Shapiro wrote: "So universal is this urge to improve on nature…that one is almost tempted to regard it as an instinct."

Hundreds of plastic practice mannequins, lips pursed in proper model pouts, float around the halls of the Energizing Summit, an annual event of the American Board of Certified Haircolorists. You don't really ever adjust to seeing the disembodied heads, be they upside down in clear plastic bags (the handle cinched tight around the neck for easier carrying), gazing out of boxes in the hotel lobby, or mounted on poles, like some kind of punishment from Tudor England.


Hairdressers from around the USA, all with stunning hair colour and impeccably maintained roots, criss-cross the poorly lit basement of the Marriott Hotel at Los Angeles Airport. They're here for two days of sessions dedicated to the science of dyeing hair.

Right away I realise that I have a lot to learn. Hair colourists, it seems, speak a different language to the rest of us. They talk of 'volume' (concentration) and 'lift' (lightening). And it turns out I have been making a faux pas. "We dye Easter eggs," one Summit instructor gently informs me. "We colour hair."


But after a day and a half, I am still waiting for some science. Then I find Tom Despenza. He has years of experience working in research and development at Clairol – a career that began when, as a microbiology student, his car broke down in front of a beauty school. He is now retired and owns his own hair colour company called Chromatics.

When I catch up with Tom at the Summit, he has been teaching his popular class 'Forget the Hype! Let's get real', which dispels the years of hearsay that makes up the beauty school curriculum.


Understanding the dyes used on hair is not as simple as understanding the colour wheel. As we all learned in art class, any colour can be obtained by mixing the three primary colours of red, yellow and blue. If you want orange, you mix yellow and red; if you want purple, you combine red and blue; and if you want brown, you mix all three.

Beauticians are taught the same thing when it comes to hair – that brown dye is a combination of three different dyes. "That's just fictitious information," says Despenza. "Brown hair colour is made up of two chemicals." Both chemicals are colourless, he explains, but they produce brown through a chemical reaction that occurs when they're combined.


An important distinction exists between colour and dye. Hairdressers are not applying pigments (at least not in the case of permanent hair dye), they are applying a mixture of chemicals to initiate dye formation. The individual dye molecules have to be linked together before they emit colour, so dyes have to sit on the head for 30 minutes to allow this reaction to occur.

In the mid-1800s, English chemist William Henry Perkin serendipitously synthesised the first non-natural dye: starting with coal tar, he was hoping to produce the malaria drug quinine but instead created mauve. His discovery revolutionised the textile industry and launched the petrochemical industry. Natural dyes just didn't have the staying power and vivid colours of the dye Perkin created. Never before had such a steadfast dye been found.


Soon after, August Hofmann (Perkin's chemistry professor) noticed that a dye he had derived from coal tar formed a colour when exposed to air. The molecule responsible was para-phenylenediamine, or PPD, the foundation of most permanent hair dyes today.

Although hair is a protein fibre, like wool, the dyeing process for textiles cannot be duplicated on the head. To get wool to take a dye, you must boil the wool in an acidic solution for an hour. The equivalent for hair is to bathe it in the chemical ammonia. Ammonia separates the protective protein layers, allowing dye compounds to penetrate the hair shaft and access the underlying pigment, melanin.


Melanin is what gives colour to human skin, eyes and hair. It's the ratio of two types of melanin – eumelanin and pheomelanin – that determines your natural hair colour. And it's the size and shape that the melanin molecules form when they cluster in the hair shaft that gives the unique tones within a hair colour. For example, blondes and brunettes have about the same ratio of eumelanin molecules to pheomelanin molecules, but blondes have fewer molecules overall. Natural blond hair also contains smaller melanin clusters, which reflect light more than the larger clusters found in dark hair.

Along with ammonia, hair dye formulas contain hydrogen peroxide, a bleaching agent. Peroxide serves two purposes: it reacts with the melanin in hair, extinguishing its natural colour, and provokes a reaction between PPD molecules. The trapped colour-emitting molecule will remain in the hair, too big to escape, and the natural colour will appear only as the hair grows out.


Early on, dye chemists realised that if they added a secondary molecule, called a coupler, they could manipulate the chemicals – a carbon here, a couple of nitrogens there – and multiply the colour choices that were available with PPD alone. Different methods have been proposed, but beauty manufacturers have yet to accept a permanent hair colour formula without PPD or its related compound p-aminophenol.

For 125 years, the oxidative reaction of PPD has been the extent of hair dye technology. Dr David Lewis, emeritus professor at the University of Leeds in the UK, thinks that this is "crazy". "Now, I know a lot about dyes and dye stuffs in the textile industry. We would never dream of using this on textiles," he says. "Primitive, archaic, all these things come to mind. Why do they persist on putting it on human heads?"


As a research professor, Lewis acted as a consultant for cosmetics companies, but he always felt uncomfortable about their insistence upon using the same old oxidative formulas. Lewis retired from academia ten years ago to launch Green Chemicals, a company that aims to develop safer consumer goods. His company introduced a more environmentally friendly flame retardant, and now Lewis wants to overhaul hair dyes.

One issue is how dyes work: Lewis says that the colour molecules become electron scavengers along the way to creating beautiful brown tresses. This need for electrons is not fulfilled exclusively by other dye molecules, so the electron scavengers also aggressively pursue the skin – causing allergic reactions and potentially damaging DNA.


Lewis is also worried that the beauty industry has too much power over consumer safety. The modern era of the Food and Drug Administration (FDA) began in 1906, when it was known as the Bureau of Chemistry. In 1930 it adopted the name we know today. The FDA has banned many types of dyes since, but it has always officially deemed coal tar dyes safe, especially for hair colouring, as long as consumers were warned of the possibility of skin irritation. To this day, coal tar dyes (which are now derived from petroleum) do not require FDA certification.

In 1979 the FDA tried to insist that hair dye manufacturers place the following label on their products: "Warning – Contains an ingredient that can penetrate your skin and has been determined to cause cancer in laboratory animals." The ingredient referred to is 4-MMPD, 4-methoxy-m-phenylenediamine, a dye with a structure very similar to PPD that, according to the FDA, showed sufficient scientific evidence of being carcinogenic. Manufacturers disagreed and threatened to sue the FDA if they pressed for the label. The FDA backed down. A few years later, manufacturers removed the carcinogenic compound from their formulas, while maintaining that 4-MMPD was safe.


There is some research into the potential risk of dyes. In 2001, researchers at the University of Southern California published a paper in the International Journal of Cancer concluding that women who frequently dye their hair were twice as likely to develop bladder cancer than those who abstain. The European Commission on Consumer Safety took note. A panel of scientists evaluated the paper, deemed it scientifically credible and recommended that the EU reassess hair dye regulations.

Over the past decade the Science Committee on Consumer Products (SCCP) – a committee of the European Commission mandated to assess and report on product safety – has collected and evaluated manufacturers' data and published opinions on a number of hair dye ingredients. This re-evaluation of hair colour ingredients by the EU has highlighted two issues.


The first is that sensitisation to dye chemicals has grown considerably. The EU has categorised 27 hair colour ingredients as sensitisers, listing 10 of them as extreme and 13 strong. Although the first exposure to a sensitiser might have no noticeable effect, a subsequent exposure – to the same chemical or to similar chemicals in temporary tattoos or textiles, for example – could lead to an allergic reaction. In the worst case, it could trigger anaphylaxis, an extreme and potentially fatal allergic response.

The second issue is a lack of data on what dye chemicals do inside the human body. When in doubt, the European Commission bans the use of a particular chemical. In 2006, then-European Commission Vice-President Günter Verheugen said in a press release: "Substances for which there is no proof that they are safe will disappear from the market. Our high safety standards do not only protect EU consumers, they also give legal certainty to European cosmetics industry." It has prohibited 22 hair dye chemicals so far – and more are likely to be added to the list, which is updated annually. Most recently the SCCP deemed 2-chloro-p-phenylenediamine, used to colour eyebrows and lashes, unsafe on the grounds of insufficient toxicology data.


When the SCCP released the findings on sensitivity in early 2007, Colipa (the European cosmetic trade association, now known as Cosmetics Europe) published a statement to "reinforce its confidence in the safety of hair dyes". Although stating their support of the European Commission's ongoing work to evaluate the safety of hair dyes, they argued that the dye chemicals were being tested in isolation and that the findings did not give an indication of the health risks the chemicals could pose if used in consumer products as instructed.

Scientists working for the industry continue to point out that no undisputed epidemiological studies show a significant risk of cancer among people who colour their hair. Unless you look at a population that is exposed to hair dye every day: hairdressers. Hairdressers have a 5 per cent greater chance of contracting bladder cancer than the general population.


It struck me that there was no mention of the safety of hair dye chemicals during any of the instructional classes I attended at the Energizing Summit. When I overheard a student being advised to think about her long-term health as a hairdresser, I looked up to see whether it related to contact with dyes (studies have shown that wearing gloves greatly reduces the amount of dye compounds absorbed into the body). But it turned out that the student was being counselled on her wrist position, not the use of gloves.

In the 1970s, anthropologist Justine Cordwell wrote a paper entitled 'The very human arts of transformation'. In it, she wrote: "The anthropological analysis of clothing and adornment should be based on the assumption that mankind, from earliest times, has probably regarded the human body as the primary form of sculpture – and not been particularly pleased with what he has seen."


Indeed, archaeological evidence shows that the use of dyes by humans dates back to the Palaeolithic period. Early humans used the iron oxide contained in dirt to decorate their dwellings, textiles and bodies with the colour red. It wasn't too long until they applied the dyes to their heads.

Ancient Egyptians dyed their hair, but rarely did so while it was on their heads. They shaved it off, then curled and braided it to fashion wigs to protect their bald heads from the sun. Black was the most popular colour until around the 12th century BCE, when plant material was used to colour the wigs red, blue or green, and gold powder was used to create yellow.


Of natural dyes, henna endures. The ancients also used saffron, indigo and alfalfa. But natural dyes only coat the hair temporarily, and people wanted chemically altered tresses. Analysing hair samples has revealed that the Greeks and Romans used permanent black hair dye thousands of years ago. They mixed substances that we know today as lead oxide and calcium hydroxide to create a lead sulphide nanoparticle, which forms when the chemicals interact with sulphur linkages in keratin, a protein in hair. When the direct application of lead proved too toxic, the Romans changed their black dye formula to one made by fermenting leeches for two months in a lead vessel.

Prostitutes during the early years of the Roman Empire were required to have yellow hair to indicate their profession. Most wore wigs, but some soaked their hair in a solution made from the ashes of burnt plants or nuts to achieve the colour chemically. Meanwhile, Germans coloured their hair red by applying a mixture of beechwood ash and goats' fat.


With the development of the scientific method in the early modern period, dyers took a more analytical approach to changing hair colour, testing the efficacy and safety of new formulas. Delights for Ladies, a recipe book of household essentials published in the early 1600s, recommends using Oyle of Vitrioll to colour black hair chestnut. The book cautions to avoid touching the skin – sound advice given that today we know Oyle of Vitrioll as sulphuric acid.

The fashion for Italian blondes repeated itself – as hair colour trends do – several hundred years later when, in the 1700s, Venetian women would recline in the sun on specially built terraces with their hair drenched in corrosive solutions of lye to achieve golden locks. Blond hair was no longer limited to prostitutes.


Yet dyes were used for more than fashion or to signify occupation. Cordwell identifies several instances where hair colour was changed for other reasons; for example, Afghans believed that dyeing their hair red with henna could cure a bad headache.

Beauty is a multi-billion-pound industry that's continuing to grow. According to one industry report, cosmetics manufacturing will have brought in $255 billion (£155 billion) in revenue globally in 2014. The industry remained stable through the recession and, as incomes increase with recovery, demand for high-priced beauty products means that global profits are estimated to increase to $316 billion by 2019.


Globally, haircare products are the largest portion of the beauty industry and secure nearly a quarter of industry revenue. In the USA, within hair and nail salons, hair-colouring services account for 18 per cent of revenue. An estimated 70 per cent of women in the USA use hair colouring products.

Reflecting on the heritage of hair dyes, you can't help but ask: why do so many people still colour their hair? Why would someone go through the rigmarole and tolerate the expense, the itching and the smell? Whatever drives our desire to change the colour of our hair, one thing is certain: people have deep emotional ties to what covers their scalps.


This is clearly true for Barclay Cunningham. At just 12 years old, she began experimenting with her hair, using a spray-in hair-lightening chemical. As an adult, she searched for years for the right hair colour. "Never once has it occurred to me to simply not dye my hair," Barclay says. "The 'me' of hair colour happens to come out of a box. The 'me' that grew out of my head was not right."

This article first appeared on Mosaic and is republished here under Creative Commons license. Image by Wellcome Images via Creative Commons license.