Newly developed hair dyes designed to prevent allergic reactions
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An international team of researchers has developed hair dyes that may be less likely to cause the allergic reactions in users that can occur with traditional dyes, according to a study published in ACS Sustainable Chemistry & Engineering.
Often used in permanent hair dye, paraphenylenediamine (PPD) turns hair a dark color that won’t wash out over time via a chemical reaction. Yet this reaction also may produce compounds that bind proteins in the user’s skin and can cause eczema, facial swelling, allergic contact dermatitis and other reactions including serious systemic toxicity.
“I have seen a quite a lot of patients suffering severe reactions to hair dye,” study researcher Paul Bigliardi, MD, professor and director of the dermato-allergy division in the department of dermatology at University of Minnesota Medical School, told Healio.
“It’s one of the strongest reactions you can have. Your whole face blows up. You’ll get eczema,” he continued. “These patients cannot use PPD-based hair dyes anymore. They have no alternatives.”
Also, PPD may sensitize users to other substances such as those broadly found in sunscreens and cosmetics and in common pigment and ink compounds. However, proposed alternatives generally are not water soluble, and their safety is not well understood.
Because PPDs are small molecules, Bigliardi said, he challenged his colleagues to create larger molecules that include the desired colors without entering the skin.
“He asked about ways not to let chemicals pass through the skin, which is the opposite of what we normally try to do with drugs,” study researcher Gopalakrishnan Venkatesan, PhD, research fellow in the department of pharmacy at National University of Singapore and senior postdoctoral researcher at Singapore-MIT Alliance for Research & Technology Centre, told Healio.
The researchers created seven dyes by modifying the aromatic amine core of PPD to give these compounds a lower binding affinity to skin proteins to prevent immune responses and cytotoxicity. Also, they added strategic hydrophilic functional groups to the dyes to increase their water solubility from 6.5% to 10%. The dyes were designed to yield a naturally black color without hydrogen peroxide or other oxidizing agents.
All seven dyes permanently colored hair samples in hues ranging from pinks to blacks that did not fade after 3 weeks of daily washing. They also generated a reduced inflammatory response in cells compared with PPD, the researchers said.
Five of the dyes also were “weak” skin sensitizers (17.2% ± 2.3% to 22.1% ± 1.7%), the researchers wrote. They did not induce IL-8 and IL-1alpha cytokines’ secretion nor overexpressed CD54 and CD86 sensitization markers in THP-1 dendritic cells. PPD, meanwhile, is considered a “moderate” sensitizer.
These five dyes also exhibited three orders of magnitude lower permeation in porcine ear skin than PPD and delivered a better overall toxicological profile, according to the researchers.
“This project took several attempts and chemical modifications, but we finally obtained compounds with good dyeing properties and minimal penetration through the skin,” Venkatesan said. “Also, differently from common permanent dyes, these dyes work even without in situ activation through oxidation, thus avoiding the need to use strong oxidizers that are known to damage the hair shaft.”
According to the researchers, the O-methyl chain attributes of these five dyes are essential to their improved aqueous solubility, dyeing efficacy and safety profile, making them preferable alternatives to PPD.
Next, the researchers aim to convert these aqueous dyes into a product such as a rinse-off cream and to explore the spectrum of colors that they could obtain by combining different dyes. The researchers also are now conducting patch tests of these new dyes with human subjects with known allergies.
“So far, it looks like we have a compound that doesn’t seem to induce an allergy in these patients who have a strong allergy to PPD,” Bigliardi said. “That has to be double confirmed with clinical trials and clinical use, but this is very promising.”
Bigliardi expects this pilot trial to be finished by midsummer. Commercialization may be in the dyes’ future as well.
“We are flexible in this regard, and we are open to licensing out our dye or even codeveloping a product with companies,” Venkatesan said. “Currently, a few companies are assessing our dyes and, hopefully, they will be keen on bringing them to the next level.”
For more information:
Paul Bigliardi, MD, can be reached at pbigliar@umn.edu.
Gopalakrishnan Venkatesan, PhD, can be reached at gopal.venkatesan@u.nus.edu.
Reference:
Perspective
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The historic rate of hair dye allergy is quite high, although dropping as a result of regulatory restrictions on PPD-based dyes (that is, less than 2% PPD content). The incidence of severe sensitization or anaphylaxis is much lower than “regular” skin sensitization.
Given the high demand for hair dyes and its multibillion-dollar market, even a low rate of allergies or sensitization can be significant. The problem with cross reactions with common “-caine” anesthetics is especially concerning.
All seven dyes showed possibly reduced allergenic activity in in vitro tests as well as reduced skin permeation. I would call that a significant improvement compared with existing dyes.
Based on my knowledge, allergic and skin sensitization reactions can be predicted very well with in vitro or new approach methods, with sensitization tests equal to or better than human testing. However, one cannot state that skin sensitization is low based on THP-1 cell results alone, which appears to be stated in the study’s conclusions.
Safer dyes should maintain their efficacy, with dyeing ability similar to or better than existing dyes and all their color varieties. This needs to be addressed further so we do not end up specifying higher concentrations of alternative dyes.
This study did not fully explore the immunoreactive and sensitization potential of these dyes, however. A few more in vitro tests would have added significant confidence in the overall conclusion, which just needs more “justification,” as explained by Alves and colleagues.
Further, these dyes are not used solo but often in combination with other chemicals. These “activated” mixtures should also be evaluated to ensure that chemical intermediates do not enhance any allergic/sensitization response.
Overall, this looks promising. But as always, further research will be needed prior to commercialization.
Perspective
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PPD is the most widely used chemical to permanently dye hair, but it can also cause allergic skin reactions. Although the overall incidence of allergy to PPD in the general population is relatively low, PPD allergy can significantly impact the livelihood of salon workers and hairdressers.
All seven of the aromatic amines tested showed low to no sensitization potential in in vitro testing compared with PPD. Single-ingredient tests are a good starting point for understanding the behavior of cosmetic ingredients. But cosmetics, including hair dyes, are complex mixtures, so this research is very preliminary and the materials are a likely long way from being commercially viable alternatives to PPD at this time.
PPD is combined with coupling compounds or direct dyes to produce a variety of shades. It would be interesting to understand the ability of these new oxidative dyes to create a palette of suitable hair colors and the stability of those colors before moving forward with in vivo safety tests to further understand allergic potential.
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