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 shopping bags.

All this so she can dye her hair.

It didn’t start out this bad. Cunningham colored 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 coloring. 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 color.

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 color that they’re willing to discreetly pick scabs from their hair, as Cunningham does, for weeks after coloring.

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.”

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Hundreds of plastic mannequins, lips pursed in 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 U.S., all with stunning hair color and impeccably maintained roots, criss-cross the poorly lit basement of the Marriott Hotel at the Los Angeles airport. They’re here for two days of sessions dedicated to the science of dyeing hair.

Right away I realize that I have a lot to learn. Hair colorists, 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 color 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-color 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 make up the beauty-school curriculum.

Understanding the dyes used on hair is not as simple as understanding the color wheel. As we all learned in art class, any color can be obtained by mixing the three primary colors 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 color is made up of two chemicals.” Both chemicals are colorless, he explains, but they produce brown through a chemical reaction that occurs when they’re combined.

An important distinction exists between color 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 color, so dyes have to sit on the head for 30 minutes to allow this reaction to occur.

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In the mid-1800s, English chemist William Henry Perkin serendipitously synthesized the first non-natural dye: Starting with coal tar, he was hoping to produce the malaria drug quinine, but instead created mauve. His discovery revolutionized the textile industry and launched the petrochemical industry. Natural dyes just didn’t have the staying power and vivid colors 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 color 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 fiber, 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 color to human skin, eyes, and hair. It’s the ratio of two types of melanin—eumelanin and pheomelanin—that determines your natural hair color. And it’s the size and shape that the melanin molecules form when they cluster in the hair shaft that give the unique tones within a hair color. 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 color, and provokes a reaction between PPD molecules. The trapped color-emitting molecule will remain in the hair, too big to escape, and the natural color will appear only as the hair grows out.

Early on, dye chemists realized 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 color choices that were available with PPD alone. Different methods have been proposed, but beauty manufacturers have yet to accept a permanent hair-color formula without PPD or its related compound, p-aminophenol.

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Wella 050 Cooling Toner with 6 percent peroxide, painted onto film and left for 20 minutes (Luke Evans)

For 125 years, the oxidative reaction of PPD has been the extent of hair-dye technology. David Lewis, an emeritus professor at the University of Leeds in the U.K., 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 10 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 color 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 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 coloring, 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 as 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 E.U. 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-color ingredients by the E.U. has highlighted two issues.

The first is that sensitization to dye chemicals has grown considerably. The EU has categorized 27 hair-color ingredients as sensitizers, listing 10 of them as extreme and 13 strong. Although the first exposure to a sensitizer 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 E.U. 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 color 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 the statement declared the organization’s support of the European Commission's ongoing work to evaluate the safety of hair dyes, it also 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 color their hair. Unless you look at a population that is exposed to hair dye every day: hairdressers. Hairdressers have a 5 percent 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.

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Schwarzkopf LIVE Color XXL Pure Purple 86, painted onto film and left for for 20 minutes (Luke Evans)

In the 1970s, anthropologist Justine Cordwell wrote a paper titled “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 color 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 color until around the 12th century BCE, when plant material was used to color 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. Analyzing 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 sulfide nanoparticle, which forms when the chemicals interact with sulfur 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 color chemically. Meanwhile, Germans colored 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 color, 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 color black hair chestnut. The book cautions to avoid touching the skin—sound advice given that today we know “Oyle of Vitrioll” as sulfuric acid.

The fashion for Italian blondes repeated itself—as hair-color trends do – several hundred years later  in the 1700s, when 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 color was changed for other reasons; for example, Afghans believed that dyeing their hair red with henna could cure a bad headache.

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Beauty is a multi-billion-dollar industry that’s continuing to grow. According to one industry report, cosmetics manufacturing will have brought in $255 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, hair-care products are the largest portion of the beauty industry and secure nearly a quarter of industry revenue. In the U.S., within hair and nail salons, hair-coloring services account for 18 percent of revenue. An estimated 70 percent of women in the U.S. use hair-coloring products.

Reflecting on the heritage of hair dyes, you can’t help but ask: Why do so many people still color 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 color 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 color. “Never once has it occurred to me to simply not dye my hair,” Barclay says. “The ‘me’ of hair color happens to come out of a box. The ‘me’ that grew out of my head was not right.”

This article appears courtesy of Mosaic.