Toluene-2,5-diamine (PTD)
Also known as: PTD; PTDS; p-toluenediamine; 2,5-diaminotoluene; 2-methyl-p-phenylenediamine; Toluene-2,5-Diamine Sulfate
INCI name: Toluene-2,5-Diamine; Toluene-2,5-Diamine Sulfate
What it does
A close chemical cousin of PPD used as the main colour-former in many permanent dyes, including some sold as 'PPD-free'. It works the same way, reacting with couplers inside the hair after mixing with peroxide.
Benefits
Similar dark, lasting colour to PPD, which lets a brand leave PPD off the label.
Concerns & Risks
A potent allergen in its own right: the American Contact Dermatitis Society named it Allergen of the Year for 2025. In a 12-clinic European study 2.8% of patients reacted to it, and most people who react to PTD also react to PPD (5 in 6 in one UK analysis). A 'PPD-free' dye built on PTD is not a safe swap for someone already allergic to PPD.
Comedogenic rating
Non-comedogenic (0)
Suitable for
People with no history of hair-dye reactions, with a skin allergy test before every use
Avoid if
You are allergic to PPD or have reacted to any permanent hair dye or black henna tattoo; your scalp is broken or irritated; you are under 16 (EU label warning)
Typical concentration
EU maximum 2.0% on the head after mixing (calculated as free base), equal to 3.6% as the sulfate salt. India: no specific limit verified. US: no maximum (coal-tar hair dye exemption).