I can’t answer for sesame, but my kid has an allergy to a specific nut, that we discovered after mum picked baby up after handling said nut, leaving bright red welts on their little body. No ingestion required.
Subsequently, immunology department, skin prick tests to identify the specific culprit, “risk of anaphylaxis” posters, and an Epipen - with risk factor based on the size of the reaction, in millimeters, to the skin prick test.
Yep: instead of a bunch of downvotes, that was exactly the right kind of response to your question. Those of us who don't have these kinds of allergies (or kids with them) would have no clue about this kind of thing, and that response summed it all up very well.
Subsequently, immunology department, skin prick tests to identify the specific culprit, “risk of anaphylaxis” posters, and an Epipen - with risk factor based on the size of the reaction, in millimeters, to the skin prick test.