The 2025 Allergen of the Year is… toluene-2,5-diamine sulfate!
Clinical Applications
By Kathryn Schwarzenberger, MD, FAAD, July 1, 2025
In this month’s Clinical Applications column, Physician Editor Kathryn Schwarzenberger, MD, FAAD, talks with Amber Reck Atwater, MD, FAAD, and Nina Botto MD, FAAD, about their recent Dermatitis paper, ‘Toluene-2,5-Diamine Sulfate: Allergen of the Year 2025.’
DermWorld: So, the 2025 Allergen of the Year is toluene-2,5-diamine sulfate (PTDS)! What is this, and where might our patients be exposed to it?
DermWorld: Why was PTDS selected as the 2025 Allergen of the Year?
Drs. Atwater and Botto: PTDS was selected as the 2025 American Contact Dermatitis Society (ACDS) Allergen of the Year to highlight its role as an allergen and its potential as an alternative for patients with contact allergy to the hair dye paraphenylenediamine (PPD). We know that about 50% of patients who are allergic to PPD are not allergic to PTDS, making this a viable alternative for some patients who are allergic to PPD.
DermWorld: How do you test for PTDS allergy? Is it included in any of the standard allergen panels? How does this impact our patients who might be allergic to it?
DermWorld: How does PTDS compare to paraphenylenediamine (PPD) in terms of allergenic potential and safety as a hair dye ingredient?
Drs. Atwater and Botto: In patch-tested populations, PPD is positive more frequently than PTDS. However, these numbers do not necessarily reflect allergenic potential or safety.
DermWorld: Do you have any recommendations for patch testing individuals who are allergic to PPD before considering PTDS as an alternative?
Drs. Atwater and Botto: In about 50% of PPD-allergic patients, PTDS can be used as an alternative hair dye. However, there is no way to predict which of these patients will be the unlucky allergic individuals. The only way to know for sure is to complete patch testing with both allergens whenever a hair dye allergy is suspected. It is important to note that most patients with PTDS allergy cannot use PPD, so the alternative option does not go both ways!
DermWorld: Are there any safe hair color alternatives we can offer our patients with PTDS allergy?
Drs. Atwater and Botto: Our Allergen of the Year article has a table that outlines hair dye products that are PPD and PTDS free. While there are multiple brands and products included in the table, some of the PPD/PTDS-free dyes include Logona Herbal Hair Color Cream and Powder, ONC Natural Colors, Organic Color Systems PPD and PTD Free Semi-Permanent Hair Color, Saach Organics Natural Hair Colour, Sante Herbal Hair Colors Powder, Surya Brasil Henna Cream, The Henna Guys Henna Hair Dye, and Vegetal Safe Color Hair Color. Because product ingredients change over time, ingredients need to be double checked before recommending them to patients with PPD and/or PTDS allergy.
DermWorld: What preventive measures can hairdressers take to minimize the risk of developing contact dermatitis from PTDS exposure?
Drs. Atwater and Botto: Hairdressers who wish to avoid contact with PTDS should wear single-use nitrile gloves. Dye penetration for nitrile gloves is about 180 minutes for PTDS and 60 minutes for PPD.
Amber Reck Atwater, MD, FAAD, is the founding owner and manager of Distinctive Dermatology, in Vienna, Virginia.
Nina Botto, MD, FAAD, serves in the department of dermatology at the University of California, San Francisco.
Their paper appeared in Dermatitis.
Dr. Atwater was previously employed by and was a prior stock owner of Eli Lilly and Company and is the director of the Contact Allergen Management Program (CAMP), an app owned and developed by the American Contact Dermatitis Society. Dr. Botto is a co-owner of Vetted Dermlab, a hypoallergenic skin care company.
Disclaimer: The views and opinions expressed in this article do not necessarily reflect those of DermWorld.
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