PPD in hairdye?

Hey there, My names Jessica, I'm 21 and I live in the West Midlands UK. I had black hair for years of which i dyed with Jet Black Nice & Easy and never had any problems with reactions. Earlier this year i decided to go blonde so I've had 3 courses of highlights to lighten my hair and now I'm bored again. I want to go a dark/rich chocolate brown color but I've read so much about people having PPD reactions that I'm scared of using anything now. Can you please tell me if you can still have a PPD reaction if the dye doesn't touch your scalp? Or any dyes that i can use that don't have this chemical in. Thanks