Electromagnetic signature

Every substance in the universe vibrates with its own unique vibrational frequency referred to as an electromagnetic fingerprint or “signature”.  When exposed to a specific substance, the body will either recognize its signature or it won’t.
Why do some people react negatively to some substances and others don’t? Why is it that person “A” has a problem with grasses, and person “B” doesn’t? It’s simply a case of person “B’s” body recognizing the grasses electromagnetic signature and person “A’s” body doesn’t. How then do we get person “A’s” body to recognize grasses?
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