P-Phenylenediamine

This ingredient is also called para-phenylenediamine or PPD. It is commonly found in hair dyes and as a substitute for henna.

PPD uses its salt components to impart a color to hair; the exact color depends on the formulation of the other ingredients.

The CDC lists PPD as a contact allergen that can cause dermatitis, or skin irritation. In 2006, this ingredient was voted Allergen of the Year by the American Contact Dermatitis Society.

The CIR (Cosmetic Ingredient Review) states this ingredient is safe to use for those who do not experience sensitization.

A review of 31 studies published between 1992 and 2005 looked at whether personal hair dye use is linked to cancer.

While one well-designed study found possible associations with certain cancers like non-Hodgkin’s lymphoma and bladder cancer, these results were not consistently seen in other studies.

Because the way each study measured hair dye use varied, a formal meta-analysis couldn’t be done.