Toluene-2,5-Diamine Sulfate: The 2025 American Contact Dermatitis Society Allergen of the Year.

The American Contact Dermatitis Society named toluene-2,5-diamine sulfate (PTDS) the 2025 Allergen of the Year. Toluene-2,5-diamine sulfate is widely used as an alternative to para-phenylenediamine (PPD) in hair dyes but is itself a potent and likely underreported contact allergen. Cross-reactivity with PPD is common. Allergic contact dermatitis to PTDS manifests similarly to PPD reactions and disproportionately affects hairdressers and individuals who frequently use hair dye. Clinical recommendations include patch testing for PTDS and PPD (with consideration of delayed readings), occupational prevention, and use of safer dye alternatives where appropriate.