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A chemical compound commonly used in permanent hair dyes has been named the 2025 Allergen of the Year by the American Contact Dermatitis Society (ACDS). Toluene-2,5-diamine sulfate (PTDS), an aromatic amine, has been recognized for its dual role as both a contact allergen and a potential alternative for individuals allergic to paraphenylenediamine (PPD), another prevalent hair dye ingredient.
The Allergen Announcement
The selection was announced at the ACDS annual meeting on March 6, where Dr. Nina Botto from the University of California, San Francisco, presented the findings. A paper published in Dermatitis by Dr. Botto and Dr. Amber Reck Atwater from Duke University highlighted the concerns surrounding PTDS.
While PTDS can serve as a safer option for some individuals allergic to PPD, it is itself a potential allergen. Despite this, it is often not included in standard patch test screening series, leading to underdiagnosis of PTDS allergies.
Prevalence and Symptoms
Data from the North American Contact Dermatitis Group for 2019-2020 and 2021-2022 showed that PTDS positivity was found in 1.6% and 1.7% of tested patients, respectively. The prevalence is notably higher among individuals frequently exposed to hair dyes, such as hairdressers. Studies have indicated PTDS sensitivity in 15.3% and 7.9% of hairdressers tested.
Symptoms of PTDS allergic contact dermatitis (ACD) often appear on the hands, hairline, periorbital area, and neck—areas that typically come into contact with hair dye. However, as seen in PPD allergies, the scalp may remain unaffected due to the presence of natural oils.
Allergy Management and Future Implications
Cross-reactions between PTDS, PTD, and PPD are common, and patients allergic to PTDS are generally unable to use PPD. However, some individuals with PPD allergies may tolerate PTDS, making it a crucial alternative.
Patients are advised to carefully check ingredient labels on hair dye products, as some “natural” or “organic” dyes still contain PTDS or PPD. Experts advocate for PTDS inclusion in standard allergy screening tests to improve diagnosis and management strategies for affected individuals.
The Importance of Awareness
Dr. Botto emphasized the need for increased awareness regarding PTDS allergies. “Hair dye allergies often present around the hairline, face, and eyelids, and severe cases may extend to the scalp,” she explained. “With expanded allergy testing, about half of PPD-allergic patients can safely use PTDS.”
For individuals allergic to both PPD and PTDS, avoiding hair dye or using henna-based alternatives is the best course of action. Further research is needed to assess the benefits of expanded patch testing and its impact on patients’ quality of life.
Disclaimer
This article is for informational purposes only and should not be taken as medical advice. If you suspect a hair dye allergy, consult a dermatologist or healthcare professional for proper diagnosis and management.
