Talk to Dermatologist on Skin Allergy

i have skin allergy issue for last many years......skin becomes red nd red patches appear...feeling itchy ,it started when i used a coloring shampoo once,i had a severe allergy on head....my face becomes red and swallowed a lot ...a secretion started from head so i had to meet a skin specialist .....according to him it was so severe attack that my life could be at risk.... after this incident i havr constant allergy issue.....i take allergy tab.Casteen after 2,3 days this reliefs me much is there any permanent solution of this issue r any allergy test which confirm allergic agent in my body also tell me suitable hair dye for my hair nd shampoo....thanks a lot