Editor’s Note: This article has been updated to improve clarity, accurately reflect the findings of the original January 2022 study, and distinguish experimental laboratory results from proven clinical benefits. The original research and its historical context have been preserved.
Key Takeaways
- Researchers developed seven experimental hair dye compounds as potential alternatives to para-phenylenediamine (PPD), a common ingredient associated with allergic reactions to permanent hair dyes.
- Five of the seven compounds showed weaker skin-sensitizing activity than conventional PPD in laboratory tests.
- The researchers also reported substantially reduced skin permeation for five compounds and lasting color on treated hair samples.
- The findings were published in ACS Sustainable Chemistry & Engineering in January 2022.
- The study did not establish that these dyes are allergy-free or safe for people with an existing PPD allergy.
Introduction
A hairstylist applies hair dye to a woman’s roots.
Hair coloring is popular among people of different ages. Some use it to cover gray hair, while others change their hair color for fashion or personal preference.
However, certain ingredients in permanent hair dyes can cause allergic reactions. Symptoms may include itching, redness, swelling, and eczema-like inflammation of the scalp, face, or surrounding skin.
One ingredient associated with these reactions is para-phenylenediamine (PPD), an aromatic amine widely used in permanent hair coloring products.
In research published in January 2022, scientists investigated whether modifying the chemical structure of PPD could produce alternative dyes with a lower potential to cause skin sensitization while preserving their coloring performance.
The researchers developed seven experimental compounds and evaluated their behavior in laboratory tests.
Their findings suggested that several modified compounds could offer a more favorable sensitization profile than conventional PPD.
However, the study did not demonstrate that these dyes eliminate allergic reactions in humans or that they are ready for routine consumer use.
The Study: Developing Alternatives to PPD
PPD is commonly used in oxidative permanent hair dyes, particularly products designed to create darker shades.
During coloring, PPD participates in chemical reactions that form pigments within the hair. These reactions help produce the lasting color that consumers expect from permanent dyes.
However, PPD and certain products formed during its oxidation can also interact with skin proteins, contributing to allergic contact dermatitis in susceptible individuals.
Researchers led by Gopalakrishnan Venkatesan explored whether modifying the chemical structure of aromatic amine dyes could reduce their potential to trigger skin sensitization.
Their study, titled Synthesis and Assessment of Non-allergenic Aromatic Amine Hair Dyes as Efficient Alternatives to Paraphenylenediamine, was published in ACS Sustainable Chemistry & Engineering in January 2022.
The researchers synthesized seven experimental aromatic amine compounds and assessed their coloring properties, skin permeation, and potential to activate biological processes associated with allergic reactions.
Five Compounds Showed Weaker Skin-Sensitizing Activity
The researchers evaluated the compounds using laboratory methods designed to investigate skin sensitization.
Five of the seven experimental compounds were classified as weak sensitizers in the reported assessments, compared with the stronger sensitizing activity associated with conventional PPD.
Selected laboratory measurements also suggested reduced activation of biological markers involved in skin sensitization.
These results were encouraging because they indicated that changing the chemical structure of PPD-related compounds might reduce some of the properties associated with allergic contact dermatitis.
However, being classified as a weak sensitizer does not mean a substance is incapable of causing an allergic reaction.
The tests did not establish that the experimental dyes would be safe for everyone, particularly people who already have a confirmed allergy to PPD.
The Modified Compounds Showed Reduced Skin Permeation
The researchers also examined how the experimental compounds passed through pig skin used as a laboratory model.
Five compounds showed approximately three orders of magnitude lower skin permeation than conventional PPD under the conditions tested.
This suggested that the chemical modifications could reduce the amount of dye-related material passing through the skin.
Lower skin permeation may be a useful characteristic when developing alternative hair dyes, but it does not independently prove that a substance is nonallergenic.
Laboratory skin models also cannot fully predict how a product will behave when repeatedly applied to the human scalp.
All Seven Compounds Produced Lasting Hair Color
An alternative to PPD must do more than demonstrate favorable laboratory safety characteristics. It must also color hair effectively.
The researchers therefore applied the experimental compounds to hair samples and evaluated their coloring performance.
All seven compounds produced lasting color, with shades ranging from pinkish tones to dark black.
The treated hair samples retained their color during laboratory washing tests conducted over three weeks.
This finding suggested that the modified compounds could preserve the cosmetic function of traditional oxidative hair dyes.
Nevertheless, lasting color on laboratory hair samples does not establish that finished products containing these ingredients would be effective or safe during ordinary consumer use.
Why PPD Can Cause Hair Dye Allergies
Hair dye allergies are often caused by allergic contact dermatitis, a delayed immune reaction that develops after the body becomes sensitized to a particular substance.
In susceptible individuals, exposure to PPD can lead to itching, redness, swelling, or blistering.
Symptoms may affect the scalp, hairline, ears, eyelids, face, or neck. They can appear hours or days after exposure.
Some people experience mild irritation, while others develop more extensive skin inflammation.
An important distinction is that not every uncomfortable reaction to hair dye is an allergy. Irritant contact dermatitis can also occur when chemicals damage or irritate the skin without involving the same allergic immune response.
A dermatologist can help distinguish between these conditions and identify potential allergens through appropriate testing.
The 2022 study focused on modifying PPD-related chemical structures to reduce laboratory indicators of skin sensitization. It did not establish that the experimental compounds would prevent allergic contact dermatitis in people.
Clinical Significance: What the Findings Mean for Consumers
The research suggested a possible route toward developing permanent hair dyes with lower skin-sensitizing potential.
This could eventually be relevant to consumers who avoid conventional hair coloring products because of previous reactions.
However, the experimental compounds were not demonstrated to be safe for individuals with known PPD allergies.
People who have experienced reactions to hair dye should not assume that a product labeled natural, hypoallergenic, or PPD-free is necessarily safe.
Alternative hair dye ingredients may also cause allergic reactions, and some chemically related substances can cross-react in sensitized individuals.
Anyone with a suspected hair dye allergy should consider consulting a dermatologist before using another coloring product.
Professional patch testing may help identify the responsible allergen and guide decisions about suitable alternatives.
If a reaction develops during or after hair coloring, the product should no longer be used, and medical advice may be necessary.
Severe facial or throat swelling, difficulty breathing, or faintness requires emergency medical attention.
The experimental compounds described in the 2022 research should not be treated as established allergy-free alternatives.
Study Limitations
Although the research produced encouraging results, several limitations are important.
First, the investigation primarily involved laboratory testing rather than clinical evaluation in people using finished hair dye products.
Second, classification as a weak sensitizer does not rule out allergic reactions, especially in individuals with an existing sensitivity to related chemicals.
Third, the skin permeation experiments used a laboratory model. Results from pig skin do not necessarily predict the effects of repeated application to human skin.
Fourth, the hair-coloring experiments evaluated treated hair samples rather than long-term cosmetic performance under varied real-world conditions.
Finally, the study did not establish the long-term safety of the experimental compounds or demonstrate that they were suitable for commercial use.
These limitations mean the findings should be understood as early-stage chemical research rather than evidence of a proven consumer product.
Conclusion
The 2022 study demonstrated that modifying aromatic amine hair dye compounds could potentially reduce their skin-sensitizing properties while preserving lasting hair color.
Five of seven experimental compounds showed weaker sensitization activity in laboratory testing, and several demonstrated substantially reduced skin permeation compared with conventional PPD.
All seven compounds also produced lasting color on hair samples.
These findings provided a promising foundation for research into alternatives to traditional permanent hair dyes.
However, the study did not establish that the modified dyes were completely safe or incapable of causing allergic reactions.
Further safety evaluation, including appropriate human studies, would be needed to determine whether these compounds could become suitable alternatives for consumers, particularly those with existing hair dye allergies.
Reference
Venkatesan, G., Dancik, Y., Neupane, Y. R., Karkhanis, A. V., Bigliardi, P., & Pastorin, G. (2022). Synthesis and Assessment of Non-allergenic Aromatic Amine Hair Dyes as Efficient Alternatives to Paraphenylenediamine. ACS Sustainable Chemistry & Engineering, 10(2), 838–849.
https://doi.org/10.1021/acssuschemeng.1c06313
