Paraphenylenediamine, 1,4-diaminobenzene (PPDA) is an aromatic amine used for permanent dyeing of hair, furs and textiles since the end of the nineteenth century. Due to its strong sensitizing properties, PPDA was banned for several dozen years in some European countries, and it is currently allowed in the concentration regulated by the European Union (EU) law.

In the majority of cases, PPDA is responsible for delayed type hypersensitivity reactions, less frequently for immediate type allergy.

In rare cases it may cause intravascular hemolysis leading to renal insufficiency .

Hair dyes are the main source of PPDA. Others include textile or fur pigments, cosmetics, tattoos, photographic developers, photocopying and printing inks, black rubber, oils and gasoline.

Paraphenylenediamine may show cross-reactions to other chemicals belonging to the so-called para group that contains an amine group on a benzene ring at the para position, which may also cause allergy to other related compounds