Acid is permenant, but located in your spinal fluid or hair and no company wants to spend the money on a hair test or a spinal tap.
E metabolizes and leaves your system within 3-4 days. Of course it might fluctuate a little based on consumption amount, metabolic rate, exercise, etc. but 4 days is a good, reasonably safe time frame.
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I can't stand the itching but I don't mind the swelling...