It has been found that the salts of some metals are adapted to the coloring of hair in a cold state; and these have been, and are, applied to change grey and red hair into brown and black.

Background: Finding alternative hair dyes for individuals allergic to para-phenylenediamine (PPD) has been difficult. Newer permanent and demipermanent hair dyes that have replaced PPD with para ...

The vast majority of reactions to hair-dye products are caused by PPD. [4–6] In past years, PPD was used in permanent hair dyes but not in semipermanent dyes. More recently, PPD has been used in ...