One morning this past October, Ms. Whitney ate a protein bar before a statistics exam. She checked the label, which noted “natural flavors” on the list of ingredients — but not sesame.

When Ms. Whitney sat down to take the exam, she started experiencing signs of an anaphylactic reaction. She readied her EpiPen.

“All of the sudden my tongue is just totally swollen and my throat is closing,” said Ms. Whitney. The reaction was so severe that she had to be injected with two doses of epinephrine before recovering at the university’s health clinic.

Stories like Ms. Whitney’s are driving a push by advocacy groups to mandate sesame labeling. The Food and Drug Administration is considering whether to add sesame to the list of major allergens.

“Sesame should be included as one of the top allergens that needs to be disclosed on labels,” said Lisa G. Gable, chief executive of Food Allergy Research & Education, a nonprofit organization based in McLean, Va.

Sesame labeling is already mandated in Canada, the European Union and Australia.

Traces amounts are difficult to track

Here’s where it gets even more complicated. Even if my box of cookies doesn’t include one of the mandated warning labels, the cookies may still contain an allergen.

Let’s say, back at the manufacturer , my cookies were put on the same conveyor belt used for almond cookies. Small bits of almond might have made it into my seemingly almond-free cookies.