Para-phenylenediamine (PPD) and its chemical cousins—called aromatice amines—trigger the allergic reactions. Eczema may show up on the face or around the hairline, and in severe cases, a patient’s face swells up leading to painful bruising that requires treatment.
More than two-thirds of hair dyes currently contain PPD or related chemicals according to researchers. According to dermatologist findings, a recent survey in London found the frequency of positive reactions to PPD in patch tests doubled over six years to 7.1% among adults with contact dermatitis.
Legislation in the European Union allows PPD to comprise up to 6% of the ingredients in hair dyes for consumers.