14K views · 130 reactions | Allergic reactionParaphenylenediamine (PPD) is a chemical substance that is widely used as a permanent hair dye.If you're allergic to PPD, your scalp and face may feel itchy and start to swell. PPD may also trigger symptoms throughout your body, such as itching, a nettle rash and generally feeling ill. These symptoms may not develop until hours, or even days, later. | Healthy Hair Journey | Facebook