Sorry to hear of your problem. This is a tricky one, you are obviously allergic to one of the main ingredients in a full colour. This can be quite dangerous if your allergy is extreme. First of all - Do not attempt to use any colouring product yourself from the major chemist chains or shops - most of them will contain the ingredient you are allergic to. I suggest you have many skin tests with other manufacturer’s colours such as Goldwell Top Chic and Colourance - Wella Koleston or Colour Touch or Schwarzkopf or Aveda colour. ...More >
Redken is an American product and are usually very strong in chemicals. The ones I have suggested are European and far more gentle on the hair and scalp. If this fails - you only have one other choice - Vegetable Colours such as Henna. Henna does come in several shades and works well on most grey hair.
On another note your allergy may well disappear in the same way it suddenly started.