In search of the perfect dye

From crushed leeches soaked in vinegar to modern chemical compounds, fashionable humans have sought ways to dye their hair for thousands of years.

It’s a messy, stinky process, which researcher Jiaxing Huang, a materials scientist at Northwestern University, U.S., compares to performing organic chemical synthesis on top of one’s head.

Dr. Huang believes he is on the trail of a solution that will make hair colouring easier and possibly safer. In a study published Thursday in the journal Chem, Dr. Huang and his colleagues report that graphene, a naturally black material, also makes a successful hair dye.

In an experiment using platinum blond hair samples and wigs, the researchers coated hair with a graphene solution that included water, vitamin C and a polymer to improve adhesion. They reported creating a natural-looking black hair shade (in contrast to the shoe-polish look that many women complain of), and that’s been something of a challenge to achieve in the hair-dye industry. The new method stayed on after 30 washings, the number necessary for a hair dye to be considered permanent.

“Your hair is covered in these cuticle scales like the scales of a fish, and people have to use ammonia or organic amines to lift the scales and allow dye molecules to get inside,” Dr. Huang says in an interview. “But lifting the cuticle makes the strands of the hair more brittle, and the damage is only exacerbated by the hydrogen peroxide that is used to trigger the reaction that synthesises the dye once the pigment molecules are inside the hair.”

Not all hair dyes use peroxide anymore, but the core chemistry is generally the same, he says.

Advantages

Graphene is a two-dimensional sheet-like material made of a single atomic layer of carbon. It is strong, thin and a great conductor of electricity and heat. When it was discovered in 2004, it was viewed as revolutionary for the electronics industry. But its thin, flexible sheets can adapt to uneven surfaces, which also makes it a good coating material, the study says. An added advantage is the elimination of static and flyaway hair on dry winter days. Another plus, Dr. Huang says, is that the graphene flakes are too large to be absorbed through the skin, unlike other ingredients generally used in current dark hair dyes that can penetrate the skin barrier.

“Because we now have a coating-based dye, we don’t have to get into the hair or change the chemical structure.It’s a nanomaterial solution to solve a chemistry problem,” he says.

Exactly how big a problem is not known. The Food and Drug Administration (FDA) reports that two ingredients that were found to cause cancer in animals are no longer used in hair dyes. But there are thousands of different chemicals in use, and of these, many have not been studied either alone or in combination with others. The FDA’s website is vague on the matter.

“We do not have reliable evidence showing a link between cancer and coal-tar hair dyes on the market today,” the agency states.

The National Cancer Institute, U.S., notes that some studies have suggested possible links to blood cancers and bladder cancers, while other studies have not found any connection. In a combined analysis of 4,461 women who had non-Hodgkin’s lymphoma, and 5,799 women who did not, researchers found that women who began using hair dye before 1980 had a 30% increase risk of non-Hodgkin’s lymphoma, compared to those who began using hair dye after 1980. The researchers were not sure if the reduced risk was due to safer dyes, or the fact that those who began using them after 1980 reflected lower cumulative exposure.

Dr. Huang said he was travelling in Europe when it occurred to him that graphene might work as a hair colouring.

“I got curious, why do people have so many different hair colours, and how do people change their hair colour?” he says said. “After I looked into this problem I realised there is a significant demand for people to dye their hair black or close to black.”

Dr. Huang says he hopes his finding leads to a useful product.

The total U.S. retail sales of at-home hair colouring products in 2016 was $1.9 billion, according to Kline & Co., a market research firm. NY Times