Really sorry to know your problem.
I also had similar allergy due to wrong clothing ,like new dress ,containing starch.
Yet ,on consulting a sin specialist, I got permanent solution. For external application I was asked to apply TRIBEN ointment, which definitely stops itching in two or 3 days.
As a smple purification method, I am following water theraphy[ drinking about 1 to 2 ltrs of water, by slow intake.
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