A bad dye job is bad enough on its own, but an itchy and irritating allergic reaction to it is even worse. And people who become allergic to hair dye can develop reactions to many other common substances, transforming a simple cosmetic treatment into a big problem. Now, researchers reporting in ACS Sustainable Chemistry & Engineering have developed a range of permanent hair dyes that avoid the allergenic properties of traditional formulations.

When applied as hair color, paraphenylenediamine (PPD) — a common ingredient in permanent dyes — undergoes a chemical reaction that turns the hair a dark color that won’t wash out over time. This reaction, however, can also produce compounds that bind proteins in the user’s skin, causing allergic responses, such as eczema and facial swelling. PPD can also sensitize users to other substances, including a compound commonly found in sunscreens and cosmetics, as well as common pigment and ink compounds. Alternatives have been proposed, but they generally are not water-soluble, and the safety of some of the compounds are not well understood. Gopalakrishnan Venkatesan and colleagues wanted to create new alternatives that would avoid the problems of PPD while still providing permanent hair coloring. 

The team prepared seven dyes based on PPD with modifications to the aromatic amine core. The modifications were chosen to potentially make the compounds less reactive toward proteins and less able to be absorbed into skin. All seven compounds permanently colored hair samples, producing a range of hues from rosy pinks to deep blacks that did not fade, even after three weeks of daily washing. The team then examined the dyes in a test commonly used in the cosmetics industry to determine if a product is a skin sensitizer. Five of the modified dyes were “weak” sensitizers, whereas PPD was “moderate.” Another test showed that the new compounds generated a reduced inflammatory response in cells compared to PPD. These results suggest that the new dyes can effectively color hair while also avoiding the potential allergenic and sensitization risks of more traditional ones.
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The authors acknowledge funding from the National University of Singapore.

Human hair can be a tool for measuring the toxicity of a city, according to London-based architects Deborah Lopez and Hadin Charbel, who have also created a textile made from hair.

​Through their research studio, Pareid, Lopez and Charbel have been analysing hair samples as a way of mapping the levels of pollution across different areas of Bangkok. Samples containing larger quantities of heavy metals indicate higher levels of environmental toxicity.

"Pollution is becoming a gigantic environmental problem," Lopez told Dezeen.

​"We were interested in the capacity of the human body to become a sensor to this, to reflect and record the environment where you live, where you breathe, and where you eat and drink."

The project, called Follicle, started out as an investigation into the potential of hair as an architectural material.

Research suggests that around 6.5 million kilos of waste human hair is produced in the UK alone every year, so Lopez and Charbel felt this material could be an untapped resource for sustainable construction.
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However, after learning about the presence of heavy metals in hair, the pair realised they could also use the substance as a research tool in cities with dangerously high levels of pollution.

They set up their first test station in Bangkok, a city that hit the headlines in early 2019 after high levels of smog forced all of its 437 schools to close.

The architects created an installation at Bangkok Design Week 2019, inviting visitors to voluntarily cut off a small amount of their hair and submit it for analysis, along with details about their day-to-day environment.
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As the hair toxicity is affected by lifestyle choices – smoking and dying your hair both led to increased metal content, for instance – visitors were asked to also provide some anonymous information about themselves.

Although there was some reluctance, Lopez and Charbel were surprised by how many people were willing to donate their hair. They ended up with hundreds of samples.

The toxicology analysis suffered long delays, as a result of the Covid-19 crisis unfolding at that time, but when they finally received the results they were able to see significant links between certain types of environment and certain metals.

For example, people who lived near major highways were found to have a notably higher volume of arsenic in their hair.
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"From that moment we were able to link these two stories together, hair toxicity and pollution in the context of Bangkok," said Charbel.

The architects have been using the information gathered to produce a "toxi-cartography", an interactive 3D map of the city that charts the varying toxicity across different areas. This is available to view on a dedicated website.
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The pair are currently presenting their research within the Spanish Pavilion at the Venice Architecture Biennale.

Going forward, Lopez and Charbel hope to be able to set up test stations in more cities, so that they can start to build up a wider understanding of the links between urban conditions and hair toxicity.

At the same time, the architects are also continuing to explore ways that waste hair can be used in building construction.
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They have used a felting machine to create a hair textile, which has featured in both the Bangkok and Venice installations. Lopez suggests that this felt could be used as an insulating material, or as some kind of acoustic panelling.

The main obstacle to overcome is the stigma surrounding the cleanliness of hair, Lopez said.

"We find it interesting that we feel comfortable with the hair of non-humans, with animal fur, but we feel so disgusted by our own hair," she stated. "We want to find a way to use this material to create something that people feel attracted to."
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Human hair has been used in a number of recent design projects, including designer Céline Arnould's ceramic vessels cast from the hair of her friends and family and a collection of bricks made from hair and manure.

DMDM hydantoin is listed by the FDA as one of the preservatives found to cause the most allergic reactions from the use of cosmetic products. It works as an antimicrobial agent and preservative in cosmetics and personal care products. It's also a “formaldehyde donor.” That means it releases a small amount of formaldehyde over time to help keep products fresh and free from contaminants. The FDA requires certain products to contain an ingredient declaration, but some ingredients may not be specifically identified and instead listed as “fragrance” or “perfume.”
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