First of all Stop using hair dyes altogether. The only truly safe option. If you want colors then follow these Dye doesn't sit on your scalp during the coloring process. Or you could, instead, apply demipermanent color to your hair ten minutes before you apply it to the rest of your hair. When choosing products, switch to non-permanent hair dyes. These generally use different, less troublesome chemicals, although about 10% of people sensitized to PPD will suffer allergic sensitivity to non-permanent dyes as well. You may well be lucky - however if your skin is inflamed from previous reactions even these may cause irritation unless you wait until any existing lesions or patches of inflammation have thoroughly settled. Henna or vegetable dyes available from 'green' shops and some chemists & hairdressers are probably the safest option.